GPS
Sorry to back-track to a long past thread, but read this in an RYA book on navigation: Accuracy and Selective Availability The inherent accuracy of Coarse Acquisition (CA) code GPS is about 20 metres ... But it is owned and operated by the American Department of Defence, who do not want potential enemies to derive the full benefit of a system that has cost them over five billion dollars. Getting that five billion dollars out of their taxpayers, however, involved making a commitment to Congress that the system would be available to civilians. This posed a dilemma that was solved by a policy known as Selective Availability (SA). SA has nothing to do with availability: it involves the introduction of deliberate errors into the time and position information carried by the CA signal, producing position errors of about 100 metres ... Differential GPS All errors can be allowed for as long as you know about them, and SA is no exception. The snag is that SA is apparently random and rapidly changing, so calibration (as for logs) or correction tables (as for compasses) do not work. The solution is to use fixed reference stations ashore to monitor the GPS signals and broadcast correction messages that can be received and automatically applied by suitably equipped GPS receivers. An advantage of this system is that it also measures and corrects several of the smaller, naturally occurring errors that affect GPS, giving accuracies in the order of 5-10 metres ... This supplementary system is called differential GPS (DGPS) and the reference stations "differential beacons". ... Most countried, including the USA, transmit DGPS as a public service, free of charge, to anyone with the necessary equipment. At present the UK is an exception, with DGPS run as a commercial venture which endeavours to make a profit by encrypting its transmissions and charging a licence fee for the software required to interpret them. I hope this doesn't duplicate too much of what was discussed before, but thought that it might explain why people's back yards tended to "wander" to some extent! All the best, David Higgon
GPS
My wife half-heard a piece on the radio this morning saying that GPS instruments would fail next week unless they had previously been modified to take account of some transmission changes. They would simply be unable to find a position. Sound a bit like the millennium bug. Does anyone have any information about this, please? Users were advised to contact their suppliers. I'm feeling lost already so can you help? Frank -- Frank Evans
GPS
Greetings fellow dialists, Once again you have supplied a deluge of answers to a question of mine, this time on GPS and its failings. What an altogether utterly amazingly erudite group of people sundial folk must be (only joking, but thanks muchly all the same). I now understand how the problem has arisen. Fortunately and by a happy chance my Magellan GPS 2000 is currently at the repairers for a quite different fault (it doesn't work) so they will presumably set it right if necessary. Thanks again. Frank -- Frank Evans
Re: GPS
Frank, The first GPS Week 1024 epoch rollover will occur at about midnight of 21-22 August. The rollover occurs every 1024 weeks. Date (and possibly time) may be incorrect for those GPS receivers that do not incorporate a workaround to deduce the new epoch. Before reading the pages below I had thought that navigation was unaffected. I think that recently manufactured receivers are more likely to incorporate a workaround and to be correct during and after this rollover. See <<http://www.2k-times.com/y2k-a118.htm>http://www.2k-times.com/y2k-a118.htm> More at <<http://www.laafb.af.mil/SMC/CZ/homepage/y2000/>http://www.laafb.af.mil/SMC /CZ/homepage/y2000/> including a list of (primarily military) receivers that have passed compliance tests for this and the Y2K problem. If this rollover presents a potential problem to you then contact your GPS receiver manufacturer (or their Web site) regarding compliance of your specific model and version. I think that a more complete Web search will locate much more on this problem. Gordon At 11:11 AM 8/16/99 , Frank Evans wrote: >My wife half-heard a piece on the radio this morning saying that GPS >instruments would fail next week unless they had previously been >modified to take account of some transmission changes. They would >simply be unable to find a position. Sound a bit like the millennium >bug. Does anyone have any information about this, please? Users were >advised to contact their suppliers. I'm feeling lost already so can you >help? Gordon Uber [EMAIL PROTECTED] Reynen & Uber Web Design http://www.ubr.com/rey&ubr/ Webmaster: Clocks and Time http://www.ubr.com/clocks/
Re: GPS
> My wife half-heard a piece on the radio this morning saying that GPS > instruments would fail next week unless they had previously been > modified to take account of some transmission changes. They would > simply be unable to find a position. Sound a bit like the millennium > bug. Does anyone have any information about this, please? Users were > advised to contact their suppliers. I'm feeling lost already so can you > help? > > Frank > -- > Frank Evans This sounds familiar. It's not a y2k problem per se, though it of a similar nature. I believe the issue is that a binary counter in the GPS systems had few enough bits that they would reach overflow during August 1999. I believe the limitation is on the satellites themselves. I don't have the book with me from which I learned this (it's "The Millennium Bug: How to Survive the Coming Chaos", by Michael S. Hyatt), nor do I remember the precise date. I will look tonight. I believe that the book said that at the time it was written no solution had been devised. It sounds like this transmission modification must be the fix that DoD devised (or perhaps the transmission modification is simply the wrap-around of the counter). I wonder whether early GPS receivers will be able to cope... It reminds me of DOS's famous "640 K memory limit. Jim --- -- | Jim Cobb | 540 Arapeen Dr. #100 | [EMAIL PROTECTED] | | Parametric| Salt Lake City, UT | (801)-588-4632 | | Technology Corp. | 84108-1202 | Fax (801)-588-4650 | --- -- Familiar things happen, and mankind does not bother about them. It requires a very unusual mind to undertake the analysis of the obvious. -- Alfred N. Whitehead
Re: GPS
Frank, Check out http://www.space.com/news/gps_rollover.html for a newspaper-style story on the GPS rollover, due to occur 22 Aug 99. Keith At 13:11 8/16/99 , you wrote: My wife half-heard a piece on the radio this morning saying that GPS instruments would fail next week unless they had previously been modified to take account of some transmission changes. They would simply be unable to find a position. Sound a bit like the millennium bug. Does anyone have any information about this, please? Users were advised to contact their suppliers. I'm feeling lost already so can you help? Frank -- Frank Evans = Keith E. Brandt, MD, WD9GET || Goodbye, cruel world that was my home- Resident in Aerospace Medicine ||there's cleaner space out here to roam. San Antonio, TX || Put my feet up on the moons of Mars- [EMAIL PROTECTED]||sit back, relax, and count the stars. http://www.dca.net/~brandt || =
Re: GPS
I wrote an in depth article on the roll-over for GPS World. It's on their Web site: http://www.gpsworld.com -- Richard Langley Professor of Geodesy and Precision Navigation On Mon, 16 Aug 1999, Keith E. Brandt, M.D. wrote: >Frank, >Check out http://www.space.com/news/gps_rollover.html for a newspaper-style >story on the GPS rollover, due to occur 22 Aug 99. > >Keith > >At 13:11 8/16/99 , you wrote: >>My wife half-heard a piece on the radio this morning saying that GPS >>instruments would fail next week unless they had previously been >>modified to take account of some transmission changes. They would >>simply be unable to find a position. Sound a bit like the millennium >>bug. Does anyone have any information about this, please? Users were >>advised to contact their suppliers. I'm feeling lost already so can you >>help? >> >>Frank >>-- >>Frank Evans > >= >Keith E. Brandt, MD, WD9GET || Goodbye, cruel world that was my home- > Resident in Aerospace Medicine ||there's cleaner space out here to roam. >San Antonio, TX || Put my feet up on the moons of Mars- >[EMAIL PROTECTED]||sit back, relax, and count the stars. >http://www.dca.net/~brandt || >= > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
GPS Accuracy
As most of you know, the US government has relaxed the restrictions on the GPS system. Supposedly the accuracy has improved from 10 meters to 1 meter. My question is, do the actual GPS units in use permit this accuracy? At the equator, one degree is 111,308 meters in length. One-meter is thus .09 (9 millionths) of a degree. Even as far north as Miami FL, a meter is about .1 (1 one-hundred-thousanths) of a degree. At my location, a meter is .107 degrees. Do the GPS units read out to 5 or 6 decimal digits of accuracy? Al Pratt 33 20 36 N 111 54 14
GPS clock accuracy
Hello >From time to time I set my watch based on the time given by my Garmin G38. My watch seems quite good in the sense that after several weeks of even months it is showing about the same time the GPS is showing. Nevertheless, I don't know how accurate my GPS is. Is there a "standard" error or deviation or something like this? How precise can I expect my GPS to be? - fernando PS - It does not seem I can tune to any reliable source of time information here in Brasília. Also, I've tried several different programs in my windows environment to set my computer clock according to some of the well-known atomic clocks in the Internet. Nevertheless, it does not seem the software are good enough. I've found difference of up to 25 seconds amongst them. -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS & war
No difference. See <http://www.op.dlr.de/~igex98op/monitor/monitor.htm> -- Richard Langley Professor of Geodesy and Precision Navigation On Fri, 26 Mar 1999, Tom Mchugh wrote: >Dear All, > >Last year there was some discussion on the List concerning >possible changes of accuracy of GPS at the time U. S. was >staging air attacks in Africa & Afghanistan, but as I recall, >there was no difinitive opinion on that matter. In light of the >current U. S. war in Jugoslavia, can anyone confirm any >differences in GPS accuracy? > > >Tom McHugh > >[EMAIL PROTECTED] > >R. R. 1, Box 896 >Fort Fairfield, ME 04742 >USA > >46? 45' 13" >67? 48' 42" > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
Re: GPS & war
Hello Tom and others I have just called my friend having regular GPS which he is using on his yacht (and dreams when I find enough time to teach him how to use sextant and do "real" navigation). His GPS piece gives him accuracy of about 15 m. This is at least what he told me at 10 PM tonight. The best I can do with my sextant in ideal conditions is 0.1 NM (Nautical Mile) which amounts to about 185.2 m. And the time issue too. GPS position is instantaneous. Single line of position using sextant may take about 30 minutes total. You have to prepare for sightings, take the precious thing out of its box, prepare stop watch or check correction of your electronic watch, go to the deck, do sightings (best if a series of 3 more), note them down, secure the sextant back to its box and then work on calculations. You start with averaging sightings, then calculations. When using classic logarithmic tables of trigonoemtric functions (1 page for 1 degree) calculations may take 10 minutes, plotting on the chart 1 minute (depending on sea conditions). Using famous Sight Reduction Tables for Marine Navigation shortens calculations to about 2 minutes but plotting then is a bit more complex and may take 2 minutes. Specialized navigation calculator is faster than the famous Tables but regular scientific calculator is not, unless programmable and programmed properly. And all this is for just one line. You need at least two lines for the position, better if you have 3 or more but do not demand too much, better may be enemy of good sometimes. Taking altitudes of bodies when passing the meridian reduces calculations to simple arithmetic but you have to spent 10 minutes, sometimes more, taking sightings. This is because you do not know exactly your position so you do not know accurately the time of the meridian passage. So you have to start well before and watch through the sextant the altitude growing. The time of standstill is few miuntes, depending on latitude and declination, and then when the altitude decreases you know that you got the meridian passage and have the latitude nearly for free. According to my friend there is a publicly available GPS device with higher accuracy that can be used as indicator if a yacht drags her anchor when anchored. The important question of dragging an anchor when anchored may be solved in another way by using lead and line. Slawek At 09:01 AM 3/26/99 EST, you wrote: >Dear All, > >Last year there was some discussion on the List concerning >possible changes of accuracy of GPS at the time U. S. was >staging air attacks in Africa & Afghanistan, but as I recall, >there was no difinitive opinion on that matter. In light of the >current U. S. war in Jugoslavia, can anyone confirm any >differences in GPS accuracy? > > >Tom McHugh > >[EMAIL PROTECTED] > >R. R. 1, Box 896 >Fort Fairfield, ME 04742 >USA > >46° 45' 13" >67° 48' 42" > Slawek Grzechnik 32 57.4'N 117 08.8'W http://home.san.rr.com/slawek
GPS and sundialling
Hello, sundiallers ! One crazy question isn't enough ! A second one came me in brain (or the thing I use as ;-)) How can a diallist use a GPS receiver to mesure the declination of a wall ? I asked me this question just some minutes before the buing of such an apparatus ! It's very practical for walking, but can this machine have an utility on sundialling ? Best regards Alain MORY 47°N 7°E 500 m
Re: GPS Accuracy
You have been given the wrong information. Before SA was turned off, the "official" accuracy was 100 metres (95%) but with 27-28 satellites, typically accuracy under good conditions was 50-60 metres (95%). Turning off SA improved accuracy from 5 to 10 times, so at most to just under 10 metres (95%) -- but not to 1 metre. For such accuracies you still need differential GPS. Most receivers can be programmed to display coordinates in decimal degrees, degrees and minutes, or degrees, minutes, and seconds. Grid coordinates (northings and eastings are also possible). There's a wealth of GPS info on the Web if you need further info. -- Richard Langley On Sat, 13 May 2000, Allan Pratt wrote: >As most of you know, the US government has relaxed the restrictions on >the GPS system. Supposedly the accuracy has improved from 10 meters to 1 >meter. My question is, do the actual GPS units in use permit this >accuracy? At the equator, one degree is 111,308 meters in length. >One-meter is thus .09 (9 millionths) of a degree. Even as far north >as Miami FL, a meter is about .1 (1 one-hundred-thousanths) of a >degree. At my location, a meter is .107 degrees. Do the GPS units >read out to 5 or 6 decimal digits of accuracy? > >Al Pratt >33 20 36 N >111 54 14 > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
Re: GPS Accuracy
Hi Allan, Garmin makes a GPS unit called eMap. It came out in March 2000. It sells for around $200. Service Merchandise is reducing the line of products they sell and they have the unit for $150 around here. These units have the 2.04 version of firmware, but with a PC cable ($30 more) you can upgrade with v 2.5 for "free". It has a moon and sun "locator" in its 2.5 version of firmware. I am not sure what that means - and would appreciate anyone shedding light on the topic. Caution: If you want maps of streets, points of interest, etc. -- you can only use Garmin Map Source MetroGuide CD ROMs (USA, United Kingdom, France, Germany, Italy,Sweden and Denmark, or Belgium, Netherlands and Luxembourg $ 124.99 each) with a PC that will load only a portion of the maps onto an 8(`$90) or 16 Meg ($125) cartridge for eMap to use. -- You could connect the GPS to something like Street Atlas on a laptop (or Palm?) , but that would defeat the purpose of a hand held mapping device. I found a lot of interesting things in the last issue of the Compendium. I was expecting some discussion on this list about some of the concepts. It is a great publication. I really liked the "interactive" dial of moving one's hand up a vertical pole - when the hand shadow hit a date line on a horizontal surface - the hand was on the hour mark. Any comments - anyone? Warren Thom (41.649N 88.096W) Allan Pratt wrote: > As most of you know, the US government has relaxed the restrictions on > the GPS system. Supposedly the accuracy has improved from 10 meters to 1 > meter. My question is, do the actual GPS units in use permit this > accuracy? At the equator, one degree is 111,308 meters in length. > One-meter is thus .09 (9 millionths) of a degree. Even as far north > as Miami FL, a meter is about .1 (1 one-hundred-thousanths) of a > degree. At my location, a meter is .107 degrees. Do the GPS units > read out to 5 or 6 decimal digits of accuracy? > > Al Pratt > 33 20 36 N > 111 54 14
GPS and Azimuth
Dear Doug and Roger, You are both right to doubt claims for 0.1 arc-second precision in azimuth using a hand-held GPS receiver but there is more to be said before dismissing GPS outright. Appropriately translated, 0.1 arcsec precision is equivalent to a 2km baseline with the end points known to 1mm. Unlikely! What you CAN do is set out a baseline of about 50m and, at each end, place matched up-market GPS receivers which are connected to the main kit close to the mid-point of the baseline. Typically, the system is left to run for 6 hours or so. All this time, both receivers are averaging their perceived positions. For any given pair of satellites all each receiver can do on its own is note the perceived difference in the clock times, which translates into a difference in distance. The locus of all points which are nearer to one satellite than another by some fixed amount gives a surface. By knowing the ephemeris data of each satellite, and taking several pairs, the intersections of these surfaces leads to a best estimate of position. In good conditions, you will end up knowing the positions of each receiver to within one or two metres. This is still pretty hopeless but now comes the clever bit... What the kit in the middle does is not merely compare perceived clock times but actually looks at the phase differences of the carrier waves from the different satellites as picked up by the two receivers. This way, they can determine the relative time differences to times corresponding to a fraction of a wavelength. This doesn't improve the estimates of the absolute positions of the two receivers at all but their RELATIVE positions can be determined to about 5mm. This is starting to look good. You are talking about 5mm in 50m or 1mm in 10,000mm which is about 20 arc-seconds or one-third of an arc-minute. With your theodolite you are (at the moment) getting an error of the order of 0.08 degrees which is about 4.8 arc-minutes. You should be able to get this down to 2 arc-minutes with practice unless there is lots of slop in your instrument!! GPS does rather better and doesn't need a clear sky. It DOES need a good view of the sky though and won't work well at street level with high buildings all round. You will need to set it up on something very solid high up. Concrete buildings don't sway as much as steel ones!! The snag is the cost of the kit. This is serious professional stuff costing between $50k and $100k. Specialist contractors who use this kit all the time are available for hire. I have used three different such contractors for big (and expensive!) sundials over the past 10 years. Frank King Cambridge, U.K. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: GPS under interference?
At 10:38 AM 12/21/98 +0200, you wrote: >Hello > > >This morning I was trying to set my watch using my GPS. Taking a fix in >my >backyard I noticed the position reported was displaced about >100 meters to the East (Latitude was the same). It aroused my >curiosity. I took the GPS to my office and read it again. >I found about 80 meters to the East again. > >This error seemed too big and too systematic to be taken >as an accident. Could it be the case that the American >government is lowering the GPS precision because of >the war? Has any one noticed any similar behaviour? My house moves occasionally 50-100 metres towards Toronto. Check the error on several days. How do you determine your exact latitude and longitude? I find that the resolution of the topographic maps is actually less than GPS. What GPS do you use? I have Garmin 45. Mike Koblic, Quesnel BC - nowhere near Toronto!
Re: GPS under interference?
GPS has been under "Selective Availability" since it was declared operational. This limits horizontal positional accuracy to 100 metres at the 95% confidence level. See http://www.cnde.iastate.edu/staff/swormley/gps/check_sa.html for more info. -- Richard Langley Professor of Geodesy and Precision Navigation On Mon, 21 Dec 1998, Fernando Cabral wrote: >Hello > > >This morning I was trying to set my watch using my GPS. Taking a fix in >my >backyard I noticed the position reported was displaced about >100 meters to the East (Latitude was the same). It aroused my >curiosity. I took the GPS to my office and read it again. >I found about 80 meters to the East again. > >This error seemed too big and too systematic to be taken >as an accident. Could it be the case that the American >government is lowering the GPS precision because of >the war? Has any one noticed any similar behaviour? > >- fernando > > >-- >Fernando Cabral Padrao iX Sistemas Abertos >mailto:[EMAIL PROTECTED] http://www.pix.com.br >mailto:[EMAIL PROTECTED] >Fone: +55 61 321-2433 Fax: +55 61 225-3082 >15? 45' 04.9" S 47? 49' 58.6" W >19? 37' 57.0" S 45? 17' 13.6" W > > > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
Re: GPS under interference?
Remember, SA is a quasi-random variation. Sometimes, the instantaneous SA error is 0. Did you monitor the position for at least 15 minutes? To the best of my knowledge, the U.S. military no longer has the need to turn off SA durirng operations. -- Richard Langley Professor of Geodesy and Precision Navigation On Mon, 21 Dec 1998 [EMAIL PROTECTED] wrote: > >On Mon, 21 Dec 1998, Fernando Cabral <[EMAIL PROTECTED]> wrote: > >>...This error seemed too big and too systematic to be taken >>as an accident. Could it be the case that the American >>government is lowering the GPS precision because of >>the war? Has any one noticed any similar behaviour? > >Hi Fernando, > >I had the same thought, so last week in the first hours of the bombing I >checked >my own GPS receiver. I found the GPS position to agree perfectly with the >topographic map position of my backyard (to the nearest arcsecond in both >coordinates, the limit of the display). Usually one of the numbers differs in >the last digit, but not that night! > >-- Roger > ** > | Roger W. Sinnott | > | Associate Editor | > | Sky & Telescope | > ** > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
Re: GPS under interference?
On Mon, 21 Dec 1998, Fernando Cabral <[EMAIL PROTECTED]> wrote: >...This error seemed too big and too systematic to be taken >as an accident. Could it be the case that the American >government is lowering the GPS precision because of >the war? Has any one noticed any similar behaviour? Hi Fernando, I had the same thought, so last week in the first hours of the bombing I checked my own GPS receiver. I found the GPS position to agree perfectly with the topographic map position of my backyard (to the nearest arcsecond in both coordinates, the limit of the display). Usually one of the numbers differs in the last digit, but not that night! -- Roger ** | Roger W. Sinnott | | Associate Editor | | Sky & Telescope | **
Re: GPS clock accuracy
Fernando, Your GPS is probably as good as it gets as far as time accuracy is concerned. However your unit must be tracking or have been locked on recently. The internal clock does not have very good long term accuracy by itself. Actual time from the gps is accurate in the microsecond level. We use gps recievers to syncronize computer networks. Bob Fernando Cabral wrote: > > Hello > > >From time to time I set my watch based on the time given by my > Garmin G38. My watch seems quite good in the sense that after > several weeks of even months it is showing about the same > time the GPS is showing. > > Nevertheless, I don't know how accurate my GPS is. Is there > a "standard" error or deviation or something like this? How precise > can I expect my GPS to be? > > - fernando > > PS - It does not seem I can tune to any reliable source of time information > here in Brasília. Also, I've tried several different programs in my windows > environment to set my computer clock according to some of the > well-known atomic clocks in the Internet. Nevertheless, it does > not seem the software are good enough. I've found difference of up > to 25 seconds amongst them. > > -- > Fernando Cabral Padrao iX Sistemas Abertos > mailto:[EMAIL PROTECTED] http://www.pix.com.br > mailto:[EMAIL PROTECTED] > Fone: +55 61 321-2433 Fax: +55 61 225-3082 > 15º 45' 04.9" S 47º 49' 58.6" W > 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS clock accuracy
I want to thank every body that helped me with my question about GPS accuracy. Based on five private messages and two public messages I think I can summarize as follows: 1) Internally GPS are very, very precise 2) The time displayed is not as precise but the error is still bellow one-second 3) Accuracy is lost quickly if unit is not tracking and is not locked on. The last information combines with my observations. If I synchronize my watch with my GPS clock Saturday or Sunday, next week-end I can expect them to differ by as much as 5 minutes. What I did not know was that my watch was so accurate: after several weeks it is still synchronized (after the unit has synchronized itself with the satellites). Thank you all guys. - fernando -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS under interference?
This is a follow-up to a four-and-a-half month old thread. Regrettably (I think that's the words diplomats prefer in these situations), it appears that my suspicions may have been correct. ) [The Washington Times] ) Published in Washington, D.C. 5am -- May 5, 1999 ) www.washtimes.com ) U.S. OKs payout for Sudan bombing 'mistake' ) ) By Jerry Seper ) THE WASHINGTON TIMES ) ) [T] he Clinton administration will not ) challenge a lawsuit filed by a Saudi ) businessman who said the bombing last year of ) his pharmaceutical plant in Sudan was a ) "mistake" based on faulty intelligence data. )The administration also agreed to release ) $24 million in assets that the businessman, ) Saleh Idris, had deposited in U.S. banks. )The Aug. 20, 1998, cruise missile attack, ) which the White House claimed was in ) retaliation for terrorist attacks on two U.S. ) embassies in Africa, came three days after ) President Clinton's appearance before a federal ) grand jury investigating his relationship with ) Monica Lewinsky. )Hours after his grand jury testimony, Mr. ) Clinton made a dramatic address to the nation ) admitting an "inappropriate relationship" with ) the former White House intern. )The White House insisted at the time it ) bombed the plant, located near Khartoum, Sudan, ) because it was tied to international terrorist ) Osama bin Laden and was producing precursors to ) VX nerve gas. Sudan countered that the plant ) manufactured only pharmaceuticals and offered ) inspection tours for U.S. officials and ) reporters. )Facing a deadline to respond to the suit, ) filed Feb. 26, the Justice Department told Mr. ) Idris' attorneys on Monday that the ) administration had ordered that the freeze ) placed on his U.S. bank accounts be lifted ) immediately. The article continues, but I will stop here... Jim Earlier I wrote: > Please know that as an American I am embarrassed by the actions of my > President. He halted the bombing two hours after the articles of > impeachment passed, calling back British bombers who were in the > process of conducting further missions (I believe the bombing did > continue after Ramadan started--can anyone confirm this--which he had > said he wanted to avoid). > > I am ashamed of his recent politically motivated bombing in Iraq as > well as his bombings in August in the Sudan and Afghanistan > immediately after his Grand Jury questioning. He also conducted a > smaller cruise-missile attack on Iraq early in the year, shortly after > the Lewinsky matter first became public. > > By all means keep an eye on his rogue international behavior and > 'convenient coincidences.' I fear you will have opportunity to test > your hypothesis. > > Jim > > > [EMAIL PROTECTED] wrote: > > > > I had the same thought, so last week in the first hours of the > > > bombing I checked my own GPS receiver. I found the GPS position > > > to agree perfectly with the topographic map position of my > > > backyard (to the nearest arcsecond in both coordinates, the limit > > > of the display). Usually one of the numbers differs in the last > > > digit, but not that night! > > > Roger > > > let's test it next time the "fly" theory comes into action again. :-) > > > - fernando > > > -- > > Fernando Cabral Padrao iX Sistemas Abertos > > mailto:[EMAIL PROTECTED] http://www.pix.com.br > > mailto:[EMAIL PROTECTED] > > Fone: +55 61 321-2433 Fax: +55 61 225-3082 > > 15=BA 45' 04.9" S 47=BA 49' 58.6" W > > 19=BA 37' 57.0" S 45=BA 17' 13.6" W
Re: GPS clock accuracy
A word of caution here, though. Some GPS receivers do not update their displays on the second and so there might be a fraction of a second delay in the displayed time. GPS receivers with a 1 pps output provide a pulse on the second with the timing accuracy mentioned below when the receiver is tracking satellites. -- Richard Langley Professor of Geodesy and Precision Navigation On Mon, 1 Feb 1999, Bob Haselby wrote: >Fernando, Your GPS is probably as good as it gets as far as time >accuracy is concerned. However your unit must be tracking or have been >locked on recently. The internal clock does not have very good long > term accuracy by itself. Actual time from the gps is accurate in the >microsecond level. We use gps recievers to syncronize computer networks. > >Bob > >Fernando Cabral wrote: >> >> Hello >> >> >From time to time I set my watch based on the time given by my >> Garmin G38. My watch seems quite good in the sense that after >> several weeks of even months it is showing about the same >> time the GPS is showing. >> >> Nevertheless, I don't know how accurate my GPS is. Is there >> a "standard" error or deviation or something like this? How precise >> can I expect my GPS to be? >> >> - fernando >> >> PS - It does not seem I can tune to any reliable source of time information >> here in Bras?lia. Also, I've tried several different programs in my windows >> environment to set my computer clock according to some of the >> well-known atomic clocks in the Internet. Nevertheless, it does >> not seem the software are good enough. I've found difference of up >> to 25 seconds amongst them. >> >> -- >> Fernando Cabral Padrao iX Sistemas Abertos >> mailto:[EMAIL PROTECTED] http://www.pix.com.br >> mailto:[EMAIL PROTECTED] >> Fone: +55 61 321-2433 Fax: +55 61 225-3082 >> 15? 45' 04.9" S 47? 49' 58.6" W >> 19? 37' 57.0" S 45? 17' 13.6" W > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
Re: GPS and sextants
I have also enjoyed this nostalgia trip on sextants. I relate to the stories of taking sights with a sextant and reducing them using Pub No 229. My interest in astronomy and sundials started with celestial navigation. Many years ago I built in my basement shop a wooden sextant that allowed me to measure altitudes to 3 minutes of a degree using a vernier scale. I was thrilled when I reduced my first noon sights even though they placed me several kilometers from my known location. These sights used a mercury blob as an artificial horizon. To use such simple devices to determine where you were in the world was amazing to me. The revelation must have been similar for the ancient Greeks measuring the diameter of the world based on shadows lengths and wells. To then learn spherical trigonometry and use altitude of stars to fix my position further enhanced this special connection to the universe. I have never used this knowledge for anything except the design of sundials. Perhaps this is why sundials hold a special fascination for me. This science is the shadow of that fascinating and much larger body of knowledge that shows who we are from where we are in this universe. Somehow I do not get the same feelings with GPS. Such instruments do not convey the same sense of place. They are like digital watches, very useful and accurate but flashing digits do not convey the same sense of time as a walking shadow or moving hands. I suspect many subscribers to this list have similar feelings. It shows with the world wide response to topics like these. Perhaps we are just showing our age, enjoying our reminiscences of the good old days. Did you know that midshipmen at Annapolis no longer have to learn to use a sextant, not even for lifeboat navigation! It is a brave new world. Please do not start a thread on slide rules. It would suck me in for sure. My log log K&E also has a special place in my psychic. However I was quite happy to burn my seven place log tables when electronic calculators came along. I even wrote a series of sundial design programs for the early TI 58/59 programable calculators if anyone is interested. Roger Bailey Walking Shadow Designs 51 N 115 W where I am enjoying a wee dram and feeling my age ;-)
Re: GPS and sextants
Dear Dialers After my recent post about GPS and sextant I got few replies to me personally. This is really amazing how sextant catches human imagination. No other instrument, whether telescope or theodolite, not to mention GPS, has such fame like sextant. Note that it is of not much use for sun dialing. It was seldom used for land navigation where you have to emulate the horizon using bowl of water, oil or mercury. On land you have zenith line instead and you may set your instrument using precise bubble levels. This is impossible at sea but there you have the horizon plane and stabilize the instrument using your hand and eye. There was one notable exception in land navigation where sextant was used as the main instrument. It was the heroic era of Arctic and Antarctic exploration, not so long ago. Causes could be few. The first one I think was that most explorers, like Amundsen, Scott, Shackleton and others, were mariners and they felt sextant with their fingertips. Second reason could be that sextant is really handy. It is not very big, nor very heavy and this was of importance when every gram of load mattered. Its set up for work on land is very fast even if not natural. You just put a bowl with mercury (maybe alcohol) on some box or block of ice to have the artificial horizon and that's it. In case of other instruments you would have to assemble tripods, attach the device, level it, orientate and other things. This would add just another activity to your daily duties and some more kilograms to your load. So sextant was certainly more convenient. BTW, when you use artificial horizon like bowl of water for sextant observations you simply measure the angle between the body and its reflection. Sextant is sometimes called "Magic Mirrors" and its influence on people having little to do with navigation certainly justifies the name. As an instrument it is not easy to use for neophites, requires determination and patience during learning period. It always requires devotion and respect from its users, whether experienced or not. GPS is a marvel of modern technology and its use is very easy. No devotion is necessary, just press the button. Because of its price it is available for everyone. Of course it wil dominate. So we are watching the beginning of an end of the glorious sextant era. Slawek Slawek Grzechnik 32 57.4'N 117 08.8'W http://home.san.rr.com/slawek
Re: GPS, spherical sundial
Hello, fabulous sundiallists ! At first, many thanks to those who gave an answer to my two strange questions (Fer, Gianni, Andrew, Fernando, Tony, Pete, Ron, Roger, Thibaud, I hope I've forgotten anybody !) I did'nt clearly expose my problem : A wall must be built above a foundation that has to be exactly oriented face to south. This wall will contain an iron armature, so that a magnetic compass will not work exactly near the wall. So I thought to give an azimuth to the workers, for example by saying : the wall must be perfectly aligned with this house angle an with this treee. I thought that it was possible to point with the GPS particular points around the wanted site. I will take relatively far points to give a better accurate guideline (e.g. some mountains twenty km far from my wall) Is it playable ? Regards Alain MORY 47°N 7°E 500 m Alsace, the country where the Sun shines in the gold wine glasses ! :-)
Re: GPS, spherical sundial
Fernando Cabral <[EMAIL PROTECTED]> writes: > Just put a vertical stake on the. You can also use a plumb line with > a node somewhere at a suitable hight. Now, at chosen intervals, > like 9 o'clock, 10 o'clock... until noon, mark in the ground where > the stake shadow ends. For each mark, draw a circle having > the stake as the center. > > In the afternoon, mark where the shadow is at each corresponding > hour. That is, 1 pm, 2 pm and 3 pm corresponding, respectively > to 11 am, 10 am and 9 am. > > Now draw a line connecting each pair of hour. Now pick one of the > lines and bisect it and draw a perpendicular line. This line should coincide > with the noon line. Also, if everything is ok, this perpendicular should > bisect all the other lines. > > If the stake if correctly placed in the vertical you will end up with a very > precise North/South line from which you can find any azimuth you > may need. (By the way, the closer the solstice on the "other" hemisphere > the more price the measuring will be). > > I do think this method is easier and more precise than the compass and > the GPS (at least in "normal" usage). I agree that a shadow method is likely to be easier and more precise than using either a compass or GPS, but I have some comments on your exposition. First, the clock time of the readings is not important. In the afternoon, you want the locations where the shadow of the nodus crosses each circle, regardless of what your watch says the time is. Second, the accuracy of the result can be compromised if the ground is not level from East to West. For high precision, you will first need to prepare a level surface for the shadows to fall on. Regards, Art Carlson
Re: GPS, spherical sundial
On Mon, 6 Mar 2000, Alain MORY wrote: > I did'nt clearly expose my problem : A wall must be built above a > foundation that has to be exactly oriented face to south. This wall will > contain an iron armature, so that a magnetic compass will not work > exactly near the wall. > So I thought to give an azimuth to the workers, for example by saying : > the wall must be perfectly aligned with this house angle an with this > treee. > > I thought that it was possible to point with the GPS particular points > around the wanted site. > I will take relatively far points to give a better accurate guideline > (e.g. some mountains twenty km far from my wall) > Is it playable ? This sounds much simpler than what I originally thought! Using a GPS handset to lay out lines at a construction site would be seriously limited by "Selective Access", the intentional pseudo-random "error" built into GPS. Any position you determine may be off by something on the order of 100 meters. Unless you use a very long measurement baseline, that error makes GPS nearly useless for this type of work. However: You mention mountain peaks ~20 kM from the site. That is a good long baseline to work with! If you have survey maps with sufficient accuracy, you need only define your site's location and that of two peaks, and you can lay out the wal very precisely. If you don't have good enough maps, then use the GPS receiver to locate the points. (Of course, that will require you to travel to those mountain peaks, with your GPS!) Dave Bell W121.9N37.3
Re: GPS, spherical sundial
Alain MORY wrote: > I did'nt clearly expose my problem : A wall must be built above a > foundation that has to be exactly oriented face to south. This wall will > contain an iron armature, so that a magnetic compass will not work > exactly near the wall. I don't see this as a problem. First, because since the wall is not built yet, its armature is not a problem. You can locate the wall using the magnetic compass. You put a line in place and you are done. The only problem I see here is how precise this measure can be. You would have to use a very good compass. And you would have to use it in a very professional way. You should take care both of magnetic declination and problems with the compass itself. You could easily end up with an error of 3 or 4 degrees, or even more. Now, even if you already have some magnetic influence on the place, this still should not be a problem. You can go as further away as you want (and can). Than you take a sight (for instance, using a engineering or militar compass) as you ask someone to put in place two stakes in the East/West direction. > So I thought to give an azimuth to the workers, for example by saying : > the wall must be perfectly aligned with this house angle an with this > treee. If the workers can follow this kind of instruction, ok. But it certainly would be easier to put the stakes in the right place and tie a line between them so the wall can just be built along the line. > I thought that it was possible to point with the GPS particular points > around the wanted site. > I will take relatively far points to give a better accurate guideline > (e.g. some mountains twenty km far from my wall) > Is it playable ? For this the compass maybe more precise than the GPS. The GPS only shows the direction when you are moving. In this case you should be moving in a straight line. Maybe repeating the movement back and forth, until you find the azimuth you want. Does not seem an easy task. Or even desirable. Now, you could use the GPS to take several fixes in far away points (5, 10 or even 20 km). The further away, the less important the error the GPS will be presenting (you should expect up to 100 m). Then, after taking the proper fixes you could connect them visually and from that line derive the azimuth you want. Finally, I don't think neither the compass nor the GPS is a good solution for the problem you have. I think for this particular case a time-proven solution of using the sun shadow is still easier, more precise and less cumbersome. Just put a vertical stake on the. You can also use a plumb line with a node somewhere at a suitable hight. Now, at chosen intervals, like 9 o'clock, 10 o'clock... until noon, mark in the ground where the stake shadow ends. For each mark, draw a circle having the stake as the center. In the afternoon, mark where the shadow is at each corresponding hour. That is, 1 pm, 2 pm and 3 pm corresponding, respectively to 11 am, 10 am and 9 am. Now draw a line connecting each pair of hour. Now pick one of the lines and bisect it and draw a perpendicular line. This line should coincide with the noon line. Also, if everything is ok, this perpendicular should bisect all the other lines. Two marks should suffice. Say, 11 am and 1 pm. Nevertheless, it is always good to have several marks. On one hand, because you may have clouds at the right time, making it impossible to draw the second mark when the time comes. If you have several marks then you will have as many opportunities to find the second mark. On the other hand, if you have several marks you can always check one against the others. This means more certainty. If the stake if correctly placed in the vertical you will end up with a very precise North/South line from which you can find any azimuth you may need. (By the way, the closer the solstice on the "other" hemisphere the more price the measuring will be). I do think this method is easier and more precise than the compass and the GPS (at least in "normal" usage). Regards - fernando > > > > Regards > > Alain MORY > > 47°N 7°E > 500 m > > Alsace, the country where the Sun shines in the gold wine glasses ! :-) -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206mailto:[EMAIL PROTECTED] PABX: +55 61 329-0202 Fax: +55 61 326-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS, spherical sundial
Arthur Carlson wrote: > Fernando Cabral <[EMAIL PROTECTED]> writes: > > I do think this method is easier and more precise than the compass and > > the GPS (at least in "normal" usage). > > I agree that a shadow method is likely to be easier and more precise > than using either a compass or GPS, but I have some comments on your > exposition. First, the clock time of the readings is not > important. In the afternoon, you want the locations where the shadow > of the nodus crosses each circle, regardless of what your watch says > the time is. You are absolutely RIGHT. My idea was not to suggest that the time was important. It is not, as you correctly say. The idea -- which I did not express correctly -- was that if you know that you made the first mark at 11 am, than the second one will be around 1 pm. So you can go for lunch and come back (say) 15 to 1 and wait until the shadow meets the circle. If you mark at 9 am then you should be back at 3 pm, so on and so forth. The only function of reading the watch is spare your time. So, thank you for clarifying this important point. > Second, the accuracy of the result can be compromised if > the ground is not level from East to West. For high precision, you > will first need to prepare a level surface for the shadows to fall on. Right again. - fernando > > > Regards, > > Art Carlson -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206mailto:[EMAIL PROTECTED] PABX: +55 61 329-0202 Fax: +55 61 326-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS and sundialling
At 19:36 1-3-00 +0100, you wrote: -Original Message/Oorspronkelijk bericht-- >How can a diallist use a GPS receiver to mesure the declination of a >wall ? if it is a very long straight wall you can walk along the wall and find out the course of this movement. Then deduct or add 90° (depends on the direction you walked. A civil GPS is not accurate enough I think for a short wall. A DGPS however should do the trick also for a short wall. > but can this machine have an utility on sundialling ? You get at least a pretty good position on your screen for the sundial - Thibaud Taudin-Chabot 52°18'19.85" North 04°51'09.45" East home email: [EMAIL PROTECTED] (attachments max. 500kB; for larger attachments contact me first)
Re: GPS, spherical sundial
use the program DIALIST (published by NASS) to find out when it is local noon at the date you want. At that date and time, perpendicular to the direction of the sun (stick in the ground and its shadow) is your east west line. Thibaud At 22:42 6-3-00 +0100, you wrote: -Original Message/Oorspronkelijk bericht-- >Hello, fabulous sundiallists ! > >At first, many thanks to those who gave an answer to my two strange >questions (Fer, Gianni, Andrew, Fernando, Tony, Pete, Ron, Roger, >Thibaud, I hope I've forgotten anybody !) > >I did'nt clearly expose my problem : A wall must be built above a >foundation that has to be exactly oriented face to south. This wall will >contain an iron armature, so that a magnetic compass will not work >exactly near the wall. >So I thought to give an azimuth to the workers, for example by saying : >the wall must be perfectly aligned with this house angle an with this >treee. > >I thought that it was possible to point with the GPS particular points >around the wanted site. >I will take relatively far points to give a better accurate guideline >(e.g. some mountains twenty km far from my wall) >Is it playable ? > > >Regards > > >Alain MORY > >47°N 7°E >500 m > >Alsace, the country where the Sun shines in the gold wine glasses ! :-) > - Thibaud Taudin-Chabot 52°18'19.85" North 04°51'09.45" East home email: [EMAIL PROTECTED] (attachments max. 500kB; for larger attachments contact me first)
Re: GPS, spherical sundial
Art Carlson contributed > >I agree that a shadow method is likely to be easier and more precise >than using either a compass or GPS, but I have some comments on your >exposition. First, the clock time of the readings is not >important. In the afternoon, you want the locations where the shadow >of the nodus crosses each circle, regardless of what your watch says >the time is. Second, the accuracy of the result can be compromised if >the ground is not level from East to West. For high precision, you >will first need to prepare a level surface for the shadows to fall on. > Several people are now using my 'Meridian Alidade' designed and made expressly to lay out local meridian lines. I found it easy to make an instrument which aligned with the meridian, it was getting that alignment accurately back onto the ground which prompted me to make the first prototype. See a picture of the instrument on my webpage at URL below. Tony Moss P.S. One ingenious fellow (and now one lady too!) uses the same instrument for determining the declination of a wall by setting it to the meridian and then rotating until perpendicular to its own image in a plane mirror set true to the wall. == \T \ / M ** ** \\- O -** ** \\ L / \ S ** *** *\\ ** ** *\\ ****** **\\ ***\\Tony Moss, Lindisfarne Sundials *\\ 43, Windsor Gardens, Bedlington, ***\\ Northumberland, England, NE22 5SY, **\\ 55° 07' 45" N1° 35' 38" W Tel/FAX +1670 823232 Mobile: 07970 208 540 Website: http://www.lindisun.demon.co.uk Horizontal, Vertical, Declining, Analemmatic, Equatorial, Polar and Capuchin Sundials individually made in solid engraving brass or phosphor bronze. Professional-quality Dialling Scales, 'engine-divided' Meridian Layout Instruments with software. Analemmatic dial plots - any size for any latitude. Graduation, re-cutting and restoration of scales. 'Lintique' patination of brass. ===
RE: GPS, spherical sundial
Hello Alain MORY
As to the magnetic compass to point NS line, the most annoying problem is
that we cannot find out how much error include, even if we would correct the
deviation. We have the problem with the compass itself and the local
magnetic influence, such as iron plates and bars in the building, electric
wires in the surrounding and iron-contented soil under the foot.
I think that the astonomical method is the most desirable, as we would say
the true NS line is defined astronomically.
1. We can use the plumb-line shadow when the sun places on the true South.
We know the time from the Annual Astronomical Tables or the Ephemeris in
each country.
2. We can use the sun's shadow being cast to the concentric circles on the
ground, as Mr. Fernando Cabral said fully in his email. This would be the
classical method.
3. If you have a transit instrument, or a theodolite, for land-surveying,
you can find out the considerably exact NS line with one-time measuring of
the sun'position. We can also use the bright stars' position. There are two
methods independently, measuring the sun's altitude and measuring the sun'
time-angle. You need the sun-glass for the instrument.
I will show you the formular calculatng the azimuth from measuring the sun's
altitude.
cos(azimuth)={sin(latitude)xsin(sun's altitude)-sin(sun's declination)}
/cos
(latitude)/cos(sun's altitude)
Latitude: we know fromGPS
Sun's altitude: we know from measuring. But we must correct the astronomical
refraction according to the temperature and the
air pressure.
Sun's declination: we know from the Astronomical Tables or the Ephemeris.
You can calculate the azimuth, and then rotating the transit or the
theodolite, you will find out the true NS line.
I hope this mail is a useful information for you.
Sumi Yoichi
Japan
[EMAIL PROTECTED]
Marathon, GPS and sundials
Dear fellows in sundialling Here I am, back from Morroco after surviving the Sahara Desert and the most gruelling foot race available for mad people like myself (http://www.sandmarathon.com, http://www.aoicimbaly.com) The first thing I read after sitting in my desk was that the American government has relinquished the controlled availabity for the GPS system. Nevertheless, the source was not reliable and does not hint to the original source. Is this a confirmed news? Best regards - fernando -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206mailto:[EMAIL PROTECTED] PABX: +55 61 329-0202 Fax: +55 61 326-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS and Azimuth
Good morning folk, I have been quietly following this strand with interest. I use GPS constantly in my research, but because of the continental-scale of my work, I don't have to worry too much about whether or not I am getting metre-level precision. It doesn't really matter to me if the locations are +/- 10 or 20 metres. My partner uses differential GPS in her research to sub-metre precision. because she is asking quite different questions, and working at a much larger scale (i.e. in detail on small areas). One day for curiosity, we set up three GPSs on a bench mark for which we had the exact surveyed location. There were no trees to interrupt the signals. GPS 1 was an old 8-satellite model, built like a brick. GPS 2 is a current 12-satellite model GPS 3 was the dGPS All GPSs agreed except for the last digit, i.e they all recorded the same location +/- the odd metre. And when I say "the odd metre" I mean +/- a couple of metres, not 10 or 20 metres. All GPSs agreed within a couple of metres of the surveyed position, but the dGPS was spot-on to less than a metre. All GPSs stabilised within a very few minutes. The handhelds "bounced around" a bit, but only the last digit (i.e. the single metres of the position), and only by a metre or two. There's no need to wait several hours, a cup of tea would provide adequate time to relax and let the satellites do their thing. (In marked contrast, in the old days of "selective availability", the position would randomly vary by up to 250 m over a period of an hour or so. But now that the uncorrupted signal is available, this no longer happens. A BIG thank you to the surveying professionals and others in the US who convinced the CIA and US military to stop being twee!) My conclusion: if you don't have trees blocking satellites, then you can get to within a metre or so using a hand-held GPS within a few minutes. Even an old brick that only picks up 8 of the many satellites available these days. I have never tried measuring / estimating bearings / azimuth with a GPS, as I have no need to. But an error of a couple of metres in position can make a big difference in a bearing to another position where there is also a similar error. Oh the price difference: GPS1 (the old brick): currently about $AUD50 (if you can find one). GPS 2: $AUD300. dGPS $AUD5000 plus extortionate monthly or annual fees for a subscription to the base-stations etc. Cheers, John John Pickard [EMAIL PROTECTED] - Original Message - From: "Frank King" <[EMAIL PROTECTED]> To: "Douglas Bateman" <[EMAIL PROTECTED]> Cc: "Roger W. Sinnott" <[EMAIL PROTECTED]>; "Sundial List" Sent: Sunday, January 28, 2007 10:20 PM Subject: GPS and Azimuth > Dear Doug and Roger, > > You are both right to doubt claims for 0.1 arc-second precision > in azimuth using a hand-held GPS receiver but there is more to > be said before dismissing GPS outright. > > Appropriately translated, 0.1 arcsec precision is equivalent > to a 2km baseline with the end points known to 1mm. Unlikely! > > What you CAN do is set out a baseline of about 50m and, at each > end, place matched up-market GPS receivers which are connected > to the main kit close to the mid-point of the baseline. > > Typically, the system is left to run for 6 hours or so. All > this time, both receivers are averaging their perceived > positions. > > For any given pair of satellites all each receiver can do on > its own is note the perceived difference in the clock times, > which translates into a difference in distance. The locus > of all points which are nearer to one satellite than another > by some fixed amount gives a surface. By knowing the > ephemeris data of each satellite, and taking several pairs, > the intersections of these surfaces leads to a best estimate > of position. > > In good conditions, you will end up knowing the positions > of each receiver to within one or two metres. This is > still pretty hopeless but now comes the clever bit... > > What the kit in the middle does is not merely compare > perceived clock times but actually looks at the phase > differences of the carrier waves from the different > satellites as picked up by the two receivers. This > way, they can determine the relative time differences > to times corresponding to a fraction of a wavelength. > > This doesn't improve the estimates of the absolute positions > of the two receivers at all but their RELATIVE positions > can be determined to about 5mm. > > This is starting to look good. You are talking about 5mm > in 50m or 1mm in 10,000mm which is about 20 arc-seconds or > one-third of an arc-minute. > > With your theodolite you are (at the moment) getting an > error of the order of 0.08 degr
The GPS zero meridian club
This is a new club consisting, so far, of two members: Frank King and myself. After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad. The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole. Doug (and Frank) --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re accuracy of GPS clock
Fernando, Good to hear that you decided to ignore Ruby! Oxygen thief! I have a rather old (i.e. 5 years!) Garmin GPS45 which I have used all over Australia, Argentina, Chile and Antarctica. Out of curiosity I have checked the clock against the time beerps on our national radio. Spot on to the second. Of course, in modern terms, only nano seconds seems to be acceptable, but for sundial work, my Garmin would not cause any noticeable errors. There is a couple of web GPS pages, and I am sure that you could find out more there. Unfortunately I can't give you the URLs at the moment, they are on my notebook, that I managed to kill. BTW, these GPS web sites also have information on the Y2K problem and GPSs. Seems that most of the "good" brands have no problem. If anyone is interested in these URLs, post a message and I will see if I can recover them from my notebook. Cheers from cloudy Sydney John Dr John Pickard Senior Lecturer, Environmental Planning Graduate School of the Environment Macquarie University, NSW 2109 Australia Phone + 61 2 9850 7981 (work) + 61 2 9482 8647 (home) Fax + 61 2 9850 7972 (work)
GPS lack soul (off topic)
Roger, Ah, the joys of a TI 59! I spent hours programming the beast to reduce my data when I was in Antarctica in 1980. I thought it was wonderful. Eventually I gave it away complete with all the modules, the mag cards, the programs and the manuals to a guy who collects them. I hope it is a good home. Slide rules. Yep, I still have mine. Have you ever looked at Bion "Mathematical instruments" printed in about 1700. Rita Shenton sells it. Persuade your family to buy it for your birthday. Gives you instructions on how to make just about every form of instrument, including slide rules. Great book. HUGE book! Almost A3 in size, and about 2" thick. Just the job for accompanying your wee dram! John PS: A flash thought just before I hit the "send" button: GPSs have no SOUL. They have no connection with anything other than the US military. (No, I am not deriding the US or any other military). Thus there is no connection with the cosmos other than a hunk of metal hanging in the sky. Not terribly romantic, but highly accurate. Yeah, well I also like soul! I suspect that is a feeling with most of us on the list.
GPS vs. the noble sextant
Hello All, Claude wrote: "The advent of satellite technology has made all this very much ahistorical question. Is it true that US Naval midshipmen no longerstudy use of the sextant? You can only hope that the GPS or radio inyour lifeboat has good batteries." I certainly hope that this is not true...I don't know for sure. I heard a story on the radio this morning about the proposed US missile defense system, and the official reaction of China to such a system. Not that I am paranoid at all, but they were quoted as saying, among other scary things, that they would attack US satellites - wouldn't that include the GPS system? Jim Tallman Sr. Designer FX Studios
Re: Marathon, GPS and sundials
Yes, it is confirmed. See <http://www.cnn.com/2000/TECH/computing/05/02/civil.gps.idg/index.html> and <http://www.spacecom.af.mil/usspacecom/gps_support/>. -- Richard Langley Professor of Geodesy and Precision Navigation On Tue, 9 May 2000, Fernando Cabral wrote: >Dear fellows in sundialling > >Here I am, back from Morroco after surviving the Sahara >Desert and the most gruelling foot race available for >mad people like myself (http://www.sandmarathon.com, http://www.aoicimbaly.com) > >The first thing I read after sitting in my desk was that >the American government has relinquished the controlled availabity >for the GPS system. Nevertheless, the source was not reliable >and does not hint to the original source. > >Is this a confirmed news? > >Best regards > >- fernando > > >-- >Fernando Cabral Padrao iX Sistemas Abertos >mailto:[EMAIL PROTECTED] http://www.pix.com.br >Fone Direto: +55 61 329-0206mailto:[EMAIL PROTECTED] >PABX: +55 61 329-0202 Fax: +55 61 326-3082 >15? 45' 04.9" S 47? 49' 58.6" W >19? 37' 57.0" S 45? 17' 13.6" W > > > === Richard B. LangleyE-mail: [EMAIL PROTECTED] Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ ===
RE: The GPS zero meridian club
Hi Doug Well there's already a very similar web site confluence.org/ This is for people trying to stand on points of exact degrees intersecting (according to WGS84) I have stood on two such points 54. N 2. W (on a lonely bit of moorland above Skipton, UK.It's very boggy , be careful ;-) ) and 52 N 5 E (Just next to a roundabout near Utrecht in the Netherlands). Trying to think back to my browsing of the site I don't recall any dial connections but then most of these confluences do lie the middle of nowhere . A more pertinent question might be what dials are on whole number lat / long lines (and why) Good luck with the membership drive! Ian Maddocks Chester, UK --- Original Message --- From: "Douglas Bateman" Sent: 30 April 2014 17:37 To: "Sundial list" Subject: The GPS zero meridian club This is a new club consisting, so far, of two members: Frank King and myself. After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad. The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole. Doug (and Frank) --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 30/04/2014 17:37, Douglas Bateman
wrote:
This is a new club consisting, so far, of two members: Frank King and myself.
After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad.
The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole.
Doug (and Frank)
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
I would be all in favour of marking the zero meridian for the whole
of its length on land, if that's the intention. Why is the
difference 90 metres ? Wikipedia says 200 metres ("102.5 metres
east of its last position") at
http://en.wikipedia.org/wiki/Meridian_%28geography%29 - see also
http://en.wikipedia.org/wiki/Prime_meridian
http://wikimapia.org/3323604/Meridian-Building says :-
"Curiously, whether by accident or design, the location of the WGS84
0° meridian is marked in Greenwich by the presence of a waste basket
on the path leading more or less due east from the observatory
containing the transit telescope."
Is it the old thing about GPS receivers being deliberately
inaccurate to preserve military secrets, or is it that dedicated GPS
receivers are more accurate than smart phones and tablets ? I know
that Harriet James used a hand held GPS receiver when measuring the
location of my house.
--
--
Richard Mallett
Eaton Bray, Dunstable
South Beds. UK
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
I wonder how well Google Earth matches up with this in terms of precision? Has
anybody ever checked?
Best,
Jim Tallman
www.spectrasundial.com
www.artisanindustrials.com
jtall...@artisanindustrials.com
513-253-5497
On Apr 30, 2014 1:57 PM, rmallett wrote:
>
> On 30/04/2014 17:37, Douglas Bateman wrote:
>>
>> This is a new club consisting, so far, of two members: Frank King and myself.
>>
>>
>>
>> After the successful British Sundial Society conference, the Sunday morning
>> was allocated to tours of the Greenwich Observatory. Quite independently,
>> Frank and I had the intention of location the WGS84 meridian, some 90m east
>> of the Greenwich brass strip. Frank had an eTrex tracker and an app on his
>> mobile phone, and I had an Axxera GPS tracker linked to my iPad.
>>
>>
>>
>> The images, if the system will let them through, show 0º 0' 0". Anyone else
>> willing to join this new exclusive club? Plenty of places to straddle the
>> line between the north pole and the south pole.
>>
>>
>>
>> Doug (and Frank)
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> ---
>>
>> https://lists.uni-koeln.de/mailman/listinfo/sundial
>>
>>
>>
>
> I would be all in favour of marking the zero meridian for the whole of its
> length on land, if that's the intention. Why is the difference 90 metres ?
> Wikipedia says 200 metres ("102.5 metres east of its last position") at
> http://en.wikipedia.org/wiki/Meridian_%28geography%29 - see also
> http://en.wikipedia.org/wiki/Prime_meridian
>
> http://wikimapia.org/3323604/Meridian-Building says :-
>
> "Curiously, whether by accident or design, the location of the WGS84 0°
> meridian is marked in Greenwich by the presence of a waste basket on the path
> leading more or less due east from the observatory containing the transit
> telescope."
>
>
> Is it the old thing about GPS receivers being deliberately inaccurate to
> preserve military secrets, or is it that dedicated GPS receivers are more
> accurate than smart phones and tablets ? I know that Harriet James used a
> hand held GPS receiver when measuring the location of my house.
>
>
> --
>
> --
>
> Richard Mallett
>
> Eaton Bray, Dunstable
>
> South Beds. UK
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
Hi Richard:
Prior to GPS each country had their own datum, but if you want GPS to truly be Global then you need a common datum.
There were other datums prior to the World Geodetic System of 1984 (WGS84,
http://en.wikipedia.org/wiki/WGS84#Longitudes_on_WGS_84) but it's the one that's the default in most GPS receivers. In
military GPS receivers there's a choice of dozens of datums. The location of zero degrees is based on the Earth's
rotation as measured by star observations that are more accurate now that we use atomic time rather than the Earth's
rotation as a clock.
http://www.prc68.com/I/DAGR.shtml
Because of plate tectonics, i.e. most of the ground is moving all the time in three dimensions, including bed rock on
mountains where telescopes have their foundations, there's really no such thing as a fixed location on Earth. When they
do laser ranging to the moon one of the corrections is the elevation of the telescope at the instant when the laser is
fired and at the instant when the return pulse is received. Called Earth Tides, and caused by the same forces that
cause ocean tides. It's measured by a very sensitive gravity meter.
http://en.wikipedia.org/wiki/Earth_tide
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
rmallett wrote:
On 30/04/2014 17:37, Douglas Bateman wrote:
This is a new club consisting, so far, of two members: Frank King and myself.
After the successful British Sundial Society conference, the Sunday morning was
allocated to tours of the Greenwich Observatory. Quite independently, Frank and
I had the intention of location the WGS84 meridian, some 90m east of the
Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile
phone, and I had an Axxera GPS tracker linked to my iPad.
The images, if the system will let them through, show 0º 0' 0". Anyone else
willing to join this new exclusive club? Plenty of places to straddle the line
between the north pole and the south pole.
Doug (and Frank)
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
I would be all in favour of marking the zero meridian for the whole of its length on land, if that's the intention.
Why is the difference 90 metres ? Wikipedia says 200 metres ("102.5 metres east of its last position") at
http://en.wikipedia.org/wiki/Meridian_%28geography%29 - see also
http://en.wikipedia.org/wiki/Prime_meridian
http://wikimapia.org/3323604/Meridian-Building says :-
"Curiously, whether by accident or design, the location of the WGS84 0° meridian is marked in Greenwich by the
presence of a waste basket on the path leading more or less due east from the observatory containing the transit
telescope."
Is it the old thing about GPS receivers being deliberately inaccurate to preserve military secrets, or is it that
dedicated GPS receivers are more accurate than smart phones and tablets ? I know that Harriet James used a hand held
GPS receiver when measuring the location of my house.
--
--
Richard Mallett
Eaton Bray, Dunstable
South Beds. UK
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 30/04/2014 19:33, Brooke Clarke wrote: Hi Richard: Prior to GPS each country had their own datum, but if you want GPS to truly be Global then you need a common datum. There were other datums prior to the World Geodetic System of 1984 (WGS84, http://en.wikipedia.org/wiki/WGS84#Longitudes_on_WGS_84) but it's the one that's the default in most GPS receivers. In military GPS receivers there's a choice of dozens of datums. The location of zero degrees is based on the Earth's rotation as measured by star observations that are more accurate now that we use atomic time rather than the Earth's rotation as a clock. http://www.prc68.com/I/DAGR.shtml Because of plate tectonics, i.e. most of the ground is moving all the time in three dimensions, including bed rock on mountains where telescopes have their foundations, there's really no such thing as a fixed location on Earth. When they do laser ranging to the moon one of the corrections is the elevation of the telescope at the instant when the laser is fired and at the instant when the return pulse is received. Called Earth Tides, and caused by the same forces that cause ocean tides. It's measured by a very sensitive gravity meter. http://en.wikipedia.org/wiki/Earth_tide Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Many thanks for that - and I thought corrections for sundials were bad enough :-) -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
Hi Ian, Exactly so, and it would be interesting to see what dials there were on such a whole number list. But the snag in all this though is that the definitions have all been changed. The arrival of satellite technology brought with it a global redefinition of the whole earth's ellipsoid and in 1999 the International Reference Meridian (IRM) was decided. This is fixed but not fixed relative to a point on the earth! It currently passes something like 5.31 arcseconds east of Airy's meridian or 102.5 metres (336.3 feet) at the latitude of the Royal Observatory, Greenwich. But since 1999 and as a consequence of continental drift and plate tectonics, the IRM has shifted a few centimetres West back towards the Airy meridian. Airy will eventually be right (again!). That must surely be a time for REAL celebration? In the UK WGS84 latitudes and longitudes are changing at about 2.5 cm per year in a north-easterly direction. In 1989, the International Reference Meridian passed an estimated 102.478 m to the east of the Airy Transit Circle at Greenwich. There’s more about this here: http://www.thegreenwichmeridian.org/tgm/articles.php?article=7 So, members of the ‘Zero Meridian Club’ are chasers after ephemera. They will need to keep coming back every few years simply to catch up... Patrick From: Ian Maddocks Sent: Wednesday, April 30, 2014 6:14 PM To: Douglas Bateman ; Sundial list Subject: RE: The GPS zero meridian club Hi Doug Well there's already a very similar web site confluence.org/ This is for people trying to stand on points of exact degrees intersecting (according to WGS84) I have stood on two such points 54. N 2. W (on a lonely bit of moorland above Skipton, UK.It's very boggy , be careful ;-) ) and 52 N 5 E (Just next to a roundabout near Utrecht in the Netherlands). Trying to think back to my browsing of the site I don't recall any dial connections but then most of these confluences do lie the middle of nowhere . A more pertinent question might be what dials are on whole number lat / long lines (and why) Good luck with the membership drive! Ian Maddocks Chester, UK --- Original Message --- From: "Douglas Bateman" Sent: 30 April 2014 17:37 To: "Sundial list" Subject: The GPS zero meridian club This is a new club consisting, so far, of two members: Frank King and myself. After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad. The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole. Doug (and Frank) --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 30/04/2014 20:19, Patrick Powers wrote: Hi Ian, Exactly so, and it would be interesting to see what dials there were on such a whole number list. But the snag in all this though is that the definitions have all been changed. The arrival of satellite technology brought with it a global redefinition of the whole earth's ellipsoid and in 1999 the International Reference Meridian (IRM) was decided. This is fixed but not fixed relative to a point on the earth! It currently passes something like 5.31 arcseconds east of Airy's meridian or 102.5 metres (336.3 feet) at the latitude of the Royal Observatory, Greenwich. But since 1999 and as a consequence of continental drift and plate tectonics, the IRM has shifted a few centimetres West back towards the Airy meridian. Airy will eventually be right (again!). That must surely be a time for REAL celebration? In the UK WGS84 latitudes and longitudes are changing at about 2.5 cm per year in a north-easterly direction. In 1989, the International Reference Meridian passed an estimated 102.478 m to the east of the Airy Transit Circle at Greenwich. There’s more about this here: http://www.thegreenwichmeridian.org/tgm/articles.php?article=7 So, members of the ‘Zero Meridian Club’ are chasers after ephemera. They will need to keep coming back every few years simply to catch up... Patrick A reason to continue ! -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
Greetings, fellow dialists,
Ian Maddocks asks what dials are on whole number lat/long lines.
During the BSS tour of Austria in 2002 we visited a pillar dial
labelled "Nieder osterreich" which claimed to be exactly at 48 deg N,
15 deg. E. It is recorded in " Austria 2002; a sundial safari.
/Bulletin of the British Sundial Society, /14, 3,//104-109, 2002"with
the following: "But following the Royal Society's motto /Nulius in
verba/ ("don't believe a word of it") our party produced several GPS
machines and the monument' position was found to be a couple of thou.
out. The suggestion that there were enough of us present to shift it
to the correct location was reluctantly rejected."
Frank 55N 1W.
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
There is an android app called "GPS averaging" that can average many
readings in order to get a more realistic value of the position.
Thibaud
At 10:44 1-5-2014, Frank Evans wrote:
Greetings, fellow dialists,
Ian Maddocks asks what dials are on whole number lat/long lines.
During the BSS tour of Austria in 2002 we visited a pillar dial
labelled "Nieder osterreich" which claimed to be exactly at 48 deg
N, 15 deg. E. It is recorded in " Austria 2002; a sundial safari.
Bulletin of the British Sundial Society, 14, 3, 104-109, 2002" with
the following: "But following the Royal Society's motto Nulius in
verba ("don't believe a word of it") our party produced several
GPS machines and the monument' position was found to be a couple
of thou. out. The suggestion that there were enough of us present
to shift it to the correct location was reluctantly rejected."
Frank 55N 1W.
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
Shame on you all - abandon this ill conceived club!! The Sun was not involved
in the conception of WGS84. You should all be expelled from the Sundial mailing
list as heretics
Kevin Karney
Freedom Cottage, Llandogo, Monmouth, NP25 4TP
Phone 01594 539 595. Mobile 07595 024 960
> On 1 May 2014, at 20:26, Thibaud Taudin Chabot wrote:
>
> There is an android app called "GPS averaging" that can average many readings
> in order to get a more realistic value of the position.
> Thibaud
>
> At 10:44 1-5-2014, Frank Evans wrote:
>> Greetings, fellow dialists,
>> Ian Maddocks asks what dials are on whole number lat/long lines.
>>> During the BSS tour of Austria in 2002 we visited a pillar dial labelled
>>> "Nieder osterreich" which claimed to be exactly at 48 deg N, 15 deg. E. It
>>> is recorded in " Austria 2002; a sundial safari. Bulletin of the British
>>> Sundial Society, 14, 3, 104-109, 2002" with the following: "But following
>>> the Royal Society's motto Nulius in verba ("don't believe a word of it")
>>> our party produced several GPS machines and the monument' position was
>>> found to be a couple of thou. out. The suggestion that there were enough of
>>> us present to shift it to the correct location was reluctantly rejected."
>>> Frank 55N 1W.
>>
>> ---
>> https://lists.uni-koeln.de/mailman/listinfo/sundial
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 02/05/2014 07:56, Kevin Karney wrote: Shame on you all - abandon this ill conceived club!! The Sun was not involved in the conception of WGS84. You should all be expelled from the Sundial mailing list as heretics Kevin Karney Freedom Cottage, Llandogo, Monmouth, NP25 4TP Phone 01594 539 595. Mobile 07595 024 960 That's a good conversation stopper ! -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 02/05/2014 07:56, Kevin Karney wrote: Shame on you all - abandon this ill conceived club!! The Sun was not involved in the conception of WGS84. You should all be expelled from the Sundial mailing list as heretics Kevin Karney Freedom Cottage, Llandogo, Monmouth, NP25 4TP Phone 01594 539 595. Mobile 07595 024 960 Wasn't there a talk about longitude at one of the BSS Conferences ? -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 30/04/2014 19:27, J. Tallman wrote: I wonder how well Google Earth matches up with this in terms of precision? Has anybody ever checked? Best, Jim Tallman www.spectrasundial.com www.artisanindustrials.com jtall...@artisanindustrials.com 513-253-5497 If you search for 51 28 39.8 N 0 00 00 E Google Earth marks the prime meridian in yellow, but as you pan, it moves around relative to the ground, so I don't understand what's going on there. Anyway, the zero longitude co-ordinates appear to be in wasteland, so there is ample opportunity for somebody to mark a line there. -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: The GPS zero meridian club
On 30/04/2014 17:37, Douglas Bateman wrote: This is a new club consisting, so far, of two members: Frank King and myself. After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad. The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole. Doug (and Frank) I have been looking up the reviews on Android GPS apps (though many of the comments are generally applicable) and it seems that (unless you use surveying equipment, or you are in the armed forces) up to ten metres accuracy is about the best that you can expect. GPS Test for Android or GPS Status for Apple (more limited - apparently Apple releases fewer secrets to developers) seem to be recommended to see how accurate you are. I guess, when you use those, the more dots you get near the centre of the circle, the better ? Apparently you should spin the device on three axes (preferably more than once each) to get a better fix (you need to get at least 4 satellites, preferably 6-9). This seems to work for most people, much better than waving in a figure of eight motion. If you travel, wait until you're outside (away from buildings, vehicles and trees) before you try to get a fix, so that it can learn the new location more quickly. Any other hints and tips ? Here are my results (indoors, and without spinning) from a few free Android apps :- Mobiwia GPS Status & Toolbox Lat. 51°52.68' N 0°35.71' W (third decimal place changing) GPS Status Test & Fix Lat. 51.878° N 0.595° W (fourth decimal place changing) GPS Averaging Lat. 51°52.68' N 0°35.71' W (third decimal place changing) Sciencewithandroid Precision GPS 51°52'41'' N 0°35'43'' W (first decimal place changing) So it seems that you can probably get precision of 0.001° or 0.01' or 1" which seems pretty good to me for free apps. -- -- Richard Mallett Eaton Bray, Dunstable South Beds. UK --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: Re accuracy of GPS clock
John Pickard wrote: > Fernando, > > Good to hear that you decided to ignore Ruby! Oxygen thief! > Thank you. > I have a rather old (i.e. 5 years!) Garmin GPS45 which I have used > all over Australia, Argentina, Chile and Antarctica. Out of curiosity > I have checked the clock against the time beerps on our national > radio. Spot on to the second. Of course, in modern terms, only nano > seconds seems to be acceptable, but for sundial work, my Garmin would > not cause any noticeable errors. I'll be 100% satisfied with one second. I just want to find when thesun norths so I can find my meridian. Since I am not a superman (yet!), I would not be able to process any higher accuracy, would I? :-) I am interested in the GPS pages, but don't worry. I am sure I can find them using Altavista, NortherLight or any other Internet portal. By the way haven't you ever travelled in Brazil? Travelling in the woods, deserts, rain forests, swamps is the kind of think I would like to have done when I was younger. Since I never did it when I was in better shape, I think I'll have to do it sometime now or in the future. I am quite interested in hearing about your trips, excursions, expeditions... - fernando -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br mailto:[EMAIL PROTECTED] Fone: +55 61 321-2433 Fax: +55 61 225-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Re: GPS and sextants (off topic)
Slawek, Couldn't agree more with you about the attraction of sextants. But, I feel I must disagree with you about your final sentence. We are not "watching the beginning of an end of the glorious sextant era". It actually ended the day the price of GPSs dropped below $1000. Now that GPS are < $US400, sextants are an interesting curiosity of the past. Same as slide rules. I mourn their passing, but I LOVE what I can do with my GPS. I don't know if I raved about it before... I have bought 1:250,000 scale topographic maps of Australia on CD (as tiff files). Load them onto my notebook. Load georef files (small files that tell the computer that a certain x y position of the cursor on the screen is the same as a certain lat/long). Attach a cable linking the GPS to the notebook. Load some software (OziExplorer, cost about $US50) and off I go. Tracks my route in real time as I drive. Plus lots of other features. More and more maps (AND nautical charts) are available on CD. The USGS sells CDs for each 1 degree square. Each CD has all the maps of that quadrangle from small scale to large scale. This is actually very inconvenient if all you want is coverage of e.g. Arizona at 1:250,000. The USGS basically told me to go to hell (a very intelligent response to a client waving his credit card at you!) They were not willing to burn a custom CD for me. So I went to a company called LandInfo and they were really helpful. Micropath appear to offer similar service. LandInfo: http://www.landinfo.com/ Micropath: http://www.micropath.com/ USGS digital raster graphics: http://mcmcweb.er.usgs.gov/drg/ Software: OziExplorer: http://www.powerup.com.au/~lornew/oziexp.html There are specific sites on the web devoted to GPS (in general, not particular brands.) These have reviews of OziExplorer and competitive software, and various hardware. Also discuss Y2K and GPS (basically no problem with most brands). I have lost my bookmark to these URLs. Sorry. So, back to sextants: buy a good one now as an investment for your grandkids. Production will rapidly cease and they will start appreciating in value. Bit sad, but then look what happened to sundials! John
Re: GPS vs. the noble sextant
At 11:54 AM 7/12/00 -0400, J.Tallman wrote: >I heard a story on the radio this morning about the proposed US missile >defense system, and the official reaction of China to such a system. Not that >I am paranoid at all, but they were quoted as saying, among other scary >things, that they would attack US satellites - wouldn't that include the GPS >system? I guess this would reduce us all to the most fundamental system of navigation, "Dead Reckoning". Roger Bailey Walking Shadow Designs N 51 W 115
Finding the meridian with a GPS
After buying an old theodolite I merrily travelled to my little farm with the firm purpose of finding the local meridian with high precision. And, as an extra, I would survey the region and have a very precise map. For no purpose at all, but what is a theodolite good for if you don't find ways to use it? They say that if you give a child a hammer she will try to fix the whole world using it. So, if an adult gives himself a theodolite, he MUST find what to do with it, right? Well, theodolite, almanac, calculator, everything in place except... the moon, the sun, the stars. It rained cats and dogs for several days. Starting on December 20 until January 5, we had plenty of water from the skies. As chance uses to have it, if I had to go to main street to buy some stuff or perhaps visit a friend, that's when we had a brief period of clear sky. But experience had taught me: if I decided to rush back home clouds would immediately fly in and start pouring the water god wanted to send us... After several days I picked up my old GPS and decided to use it to replace the stars. I chose a far away point. A tree about 1000 m from the place I set up the theodolite. I walked to it and took a reading (in fact, several readings). Then I walked back to where the theodolite was and took some readings. According to the GPS distance was a little bellow 1000m. I used the GPS to find the bearing from one point to the other. I set the limbo to 0 at that tree. From there I could find any other bearing. My reasoning was that even if the GPS would give me an error of, say, 20 meters to one side (worst case) I'd still be very close to the real azimuth. In fact, let's suppose (this was what I reasoned) I have a right triangle with two legs of 707,1 m each. The third side would be 999,99 (that is, 1000 m). Now, the angle each of the two other angles would be 45 degrees. Now, if, instead of having a leg of 707,1m I had it with 727,1, the difference in the angles would be arc tan (727,1 / 707,1) = 45,7 so, an error of less than 1 degree. Close enough for most purposes, I guess, And probabily better than the other simple methods. Of course, if I wanted to secure higher precision I could still try to go further away (terrain permiting). With a tower (or tree) 5 km away my error would be of less than 10 minutes for a GPS error of 20 m in the worst direction. I still expect to refine my findings when I have a good star in the proper position and a cloudless sky. But for the time being I am happy that I could put my o'theodolite to use. Now I am a happy (ancient) kid! - fernando -- REDUZIR, REUSAR, RECICLAR -- Dever de todos, amor aos que virão REDUCE, REUSE, RECYCLE -- Everybody's duty, love to those who are to come Fernando CabralPadrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206 mailto:[EMAIL PROTECTED] PABX: +55 61 329-0202 Fax: +55 61 326-3082 15º 45' 04.9" S (23 L 0196446/8256520) 47º 49' 58.6" W 19º 37' 57.0" S (23 K 0469898/7829161) 45º 17' 13.6" W
GPS and magnetic compasses for dial orientation.
Hi all, I have been skimming all the dial stuff lately and have seen a few comments on using GPS and Compasses for orienting sundials. On my first experimental dials I used a puck type marine hand bearing compass for alignment. I live on a hill and was able to sight to a distant object that was directly east after correcting for the magnetic variation. This happened to be a restaurant about a mile away. To align the dial (a horizontal with a square base) I just sighted along the edge of the dial to the same spot. This seemed to work ok. I figured the error using this method was probably about as good as you could do with a compass. I think that a similar technique using a GPS might give a reasonable alignment. In my case where I live on a hill and have unrestricted view (on a clear day) of sometimes 30 miles to distant peaks in the local hills and mountains, I think that the accuracy of gps would be good enough if I "locate" myself on a distant hill and have the gps calculate the bearing to my home location. The reciprocal bearing would be observed from my back yard and could be used to align a dial. The assumption of course is that the gps position error would generate a pretty insignificant bearing error if the base line distance to the identifiable peak is large when compared to the probable position error. To reduce the error to a minimum one would use two gps units simultaneously one at each location and with the judicious use of a cell phone to effect simultaneity, one could minimize the total differential error. A topographical map could also be used for alignment without actually involving a hike to the peak. For later dials (most vertical declining) I observe the time when the rising sun just grazes the surface of the dial location. This is easy and accurate. Dials are forever, Bob 33N 117W
Re: Finding the meridian with a GPS
Fernando, I am not quite sure of exactly what you were trying to determine! You need have no worries re the accuracy of your GPS. By "old GPS", I assume that you mean an 8-satellite one (like my 8 year old brick!). Have no worries about the accuracy of an 8-satellite GPS. I bought my son (an avid explorer of rugged bushland near Sydney, that involved him in a couple of epics when he went into the wrong creek, necessitating nearly 10 abseils (US = rappel) including two of 75 m on 70 m ropes!). I set it up for him before I gave it to him, and out of curiosity, I checked my old 8-satellite Garmin against the new 12-satellite Garmin. The only difference in multiple readings was in the last digit (i.e. the metres digit). This convinces me that now that the CIA (sorry, US government) has removed selective availability, you can use the old GPS with no worries at all. BTW, my staff have also tested 12-channel GPSs on surveyed points in the landscape. Again, the only difference was in the metres digit. Given that the new Garmin Etrex costs AUD $380 (i.e. probably around $US 150), this is pretty acceptable accuracy. In fact, it is damn fine accuracy. Having said all that, the little yellow thing of electronics in your hand doesn't have the same aesthetic attraction as a theodolite! Cheers, John "Far better an approximate answer to the right question which may be difficult to frame, than an exact answer to the wrong question which is always easy to ask" John W Tukey, statistician - Original Message - From: "Fernando Cabral" <[EMAIL PROTECTED]> To: "sundial mailing list" Sent: Tuesday, January 08, 2002 11:29 PM Subject: Finding the meridian with a GPS After buying an old theodolite I merrily travelled to my little farm with the firm purpose of finding the local meridian with high precision. And, as an extra, I would survey the region and have a very precise map. For no purpose at all, but what is a theodolite good for if you don't find ways to use it? They say that if you give a child a hammer she will try to fix the whole world using it. So, if an adult gives himself a theodolite, he MUST find what to do with it, right? Well, theodolite, almanac, calculator, everything in place except... the moon, the sun, the stars. It rained cats and dogs for several days. Starting on December 20 until January 5, we had plenty of water from the skies. As chance uses to have it, if I had to go to main street to buy some stuff or perhaps visit a friend, that's when we had a brief period of clear sky. But experience had taught me: if I decided to rush back home clouds would immediately fly in and start pouring the water god wanted to send us... After several days I picked up my old GPS and decided to use it to replace the stars. I chose a far away point. A tree about 1000 m from the place I set up the theodolite. I walked to it and took a reading (in fact, several readings). Then I walked back to where the theodolite was and took some readings. According to the GPS distance was a little bellow 1000m. I used the GPS to find the bearing from one point to the other. I set the limbo to 0 at that tree. From there I could find any other bearing. My reasoning was that even if the GPS would give me an error of, say, 20 meters to one side (worst case) I'd still be very close to the real azimuth. In fact, let's suppose (this was what I reasoned) I have a right triangle with two legs of 707,1 m each. The third side would be 999,99 (that is, 1000 m). Now, the angle each of the two other angles would be 45 degrees. Now, if, instead of having a leg of 707,1m I had it with 727,1, the difference in the angles would be arc tan (727,1 / 707,1) = 45,7 so, an error of less than 1 degree. Close enough for most purposes, I guess, And probabily better than the other simple methods. Of course, if I wanted to secure higher precision I could still try to go further away (terrain permiting). With a tower (or tree) 5 km away my error would be of less than 10 minutes for a GPS error of 20 m in the worst direction. I still expect to refine my findings when I have a good star in the proper position and a cloudless sky. But for the time being I am happy that I could put my o'theodolite to use. Now I am a happy (ancient) kid! - fernando -- REDUZIR, REUSAR, RECICLAR -- Dever de todos, amor aos que virão REDUCE, REUSE, RECYCLE -- Everybody's duty, love to those who are to come Fernando CabralPadrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206 mailto:[EMAIL PROTECTED] PABX: +55 61 329-0202 Fax: +55 61 326-3082 15º 45' 04.9" S (23 L 0196446/8256520) 47º 49' 58.6" W 19º 37' 57.0" S (23 K 0469898/7829161) 45º 17' 13.6" W
A list of sundials with GPS positions
I found a web page for www.waymarking.com, which is evidently a place for people to record the location of interesting things. There is a sundial catagory with 65 sundials listed. --- https://lists.uni-koeln.de/mailman/listinfo/sundial
The GPS zero meridian club - a round up
Many thanks to all who, as typical of the list, sent relevant and interesting posts. I would like to comment on some as follows: IM: the confluence website - crazy but yet more fun. RM: the old civil 'degradation' of accuracy of GPS was removed many years ago. Dedicated GPS receivers are more accurate than smart phones or tablets who use the identity of their routers to give a location, although better than just a Postcode. See more below. JT: Google Earth matches the precision in that I found the WGS84 zero line to be exactly where Frank and I were making our observations. The Google Earth cursor shows incredible precision - down to hundredths of a second of arc. Centimetre accuracy? PP: chasing after ephemera (the lat/long lines are moving over long periods, even a year). Never mind, we simply move our GPS receivers to suit! FE: the 'confluence dial' in Austria. I remember it as being rather massive and to have moved it would have strained our party... TT: GPS averaging apps. Following this I bought two, more below. KK: HERESY because the WGS84 meridian has nothing to do with the sun. The satellites have large solar panels - just think of WGS84 as being solar powered! Spin-off: the dials on the zero meridian UK, France and Spain. RM: precision with free apps. All very good, and I tried an experiment with my Axxera GPS receiver and two averaging apps (GPS Averaging and Perfect Mark) on my iPad. The Axxera quotes a CEP of ±2.5 metres, but the experiment was to see if I could determine a change in longitude by placing a 1 metre rule aligned with the latitude in a open area on my lawn. As it happens, for my latitude (51º 22' N) 1 metre corresponds to 0.001 minute of arc in longitude. The systems update every second so it was no trouble to average 100 samples for 3 sets of readings for each averaging app. For the GPS Averaging I got 0º 48.1357' and 0º 48.1367' at either end of the rule, and for the Perfect Mark 0º 48.1362' and 0º 48.1377. In other words definitely resolving a metre on the ground. I expect that repeating for another 600 readings half an hour later (all different satellites and bearings) I may have obtained higher precision still by combining both sets of data. Amazing. Thanks again for the fascinating insights. Regards, Doug PS An image of Frank King and BSS member Ian Butson recording the event of 0º 0' 0". Note the Greenwich landmarks in the background. The Greenwich meridian passes to the left of the power station chimneys. > On 30/04/2014 17:37, Douglas Bateman wrote: >> This is a new club consisting, so far, of two members: Frank King and myself. >> >> After the successful British Sundial Society conference, the Sunday morning >> was allocated to tours of the Greenwich Observatory. Quite independently, >> Frank and I had the intention of location the WGS84 meridian, some 90m east >> of the Greenwich brass strip. Frank had an eTrex tracker and an app on his >> mobile phone, and I had an Axxera GPS tracker linked to my iPad. >> >> The images, if the system will let them through, show 0º 0' 0". Anyone else >> willing to join this new exclusive club? Plenty of places to straddle the >> line between the north pole and the south pole. >> >> Doug (and Frank) --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: GPS and magnetic compasses for dial orientation.
Bob Haselby wrote: > To reduce the error to a minimum one would use two gps units > simultaneously one at each location and with the judicious use of a cell > phone to effect simultaneity, one could minimize the total differential > error. For good topographic conditions like yours the technique you suggest should work ok. Nevertheless... > A topographical map could also be used for alignment without > actually involving a hike to the peak. If you have a topo map that is refined enough (and has a proper scale), they you would need only the map itself and an alidade. I think. - fernando -- Fernando Cabral Padrao iX Sistemas Abertos mailto:[EMAIL PROTECTED] http://www.pix.com.br Fone Direto: +55 61 329-0206mailto:[EMAIL PROTECTED] PABX: +55 61 329-0202 Fax: +55 61 326-3082 15º 45' 04.9" S 47º 49' 58.6" W 19º 37' 57.0" S 45º 17' 13.6" W
Time question on GPS TIME and leap second.
Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" To: "Robert Kellogg" Cc: "sundial list" Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.24219 days, when it's really 365.24217 mean days long. ...for the purposes of a calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, and due to gradual change in the lengths of all the tropical years, including the MTY. But that doesn't mean we have to intentionally add avoidable error. > Contemplating decoupling UTC from the rotation of the earth (ie necessity > of being within .9 sec of UT1) likewise has significant consequences. > Let's let the IAU chart the future of time. Sure, but it isn't necessary to base a calendar on a day that isn't today's mean solar day. Michael Ossipoff > Dennis and Ken, if you're listening to this discussion, please chime in. > > > On 1/29/2017 12:27 PM, sundial-requ...@uni-koeln.de wrote: > >> Send sundial mailing list submissions to >> sundial@uni-koeln.de >> >> To subscribe or unsubscribe via the World Wide Web, visit >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> or, via email, send a message with subject or body 'help' to >> sundial-requ...@uni-koeln.de >> >> You can reach the person managing the list at >> sundial-ow...@uni-koeln.de >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of sundial digest..." >> >> >> Today's Topics: >> >> 1. Re: Why we should reform the Calendar (Michael Ossipoff) >> >> >> -- >> >> Message: 1 >> Date: Sun, 29 Jan 2017 12:27:56 -0500 >> From: Michael Ossipoff >> To: Dan-George Uza >> Cc: sundial list >> Subject: Re: Why we should reform the Calendar >> Message-ID: >> > gmail.com> >> Content-Type: text/plain; charset="utf-8" >> >> >> Here are two (unimportant) objections to the Nearest-Monday year-start >> system: >> >> 1. It's based on the Gregorian leapyear-rule, meaning that it isn't >> self-contained & free-standing. Mostly an aesthetic objection, and I don't >> consider it important. >> >> 2. It inherits certain properties of the Gregorian Calendar, which could >> otherwise be adjustable, choose-able. This, too, I consider only an >> aesthe
Re: The GPS zero meridian club - a round up
Hi Doug: I recently got a used CSI LGBX Pro DGPS Receiver. This is a CSI long wave beacon receiver with an integrated Ashtech 12 channel GPS receiver iwth an antenna that receives both of them. The display option with the most resolution is dddmm. and it seems to be good to less than one foot without averaging. Note that the LF corrections are coming from an Earth station that's not to far from where you are receiving them. The WAAS differential corrections are for a much larger area and may not be as accurate, don't know as so far I don't have a WAAS corrected GPS. http://www.prc68.com/I/LGBXcsiDGPS.html Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Douglas Bateman wrote: Many thanks to all who, as typical of the list, sent relevant and interesting posts. I would like to comment on some as follows: IM: the confluence website - crazy but yet more fun. RM: the old civil 'degradation' of accuracy of GPS was removed many years ago. Dedicated GPS receivers are more accurate than smart phones or tablets who use the identity of their routers to give a location, although better than just a Postcode. See more below. JT: Google Earth matches the precision in that I found the WGS84 zero line to be exactly where Frank and I were making our observations. The Google Earth cursor shows incredible precision - down to hundredths of a second of arc. Centimetre accuracy? PP: chasing after ephemera (the lat/long lines are moving over long periods, even a year). Never mind, we simply move our GPS receivers to suit! FE: the 'confluence dial' in Austria. I remember it as being rather massive and to have moved it would have strained our party... TT: GPS averaging apps. Following this I bought two, more below. KK: HERESY because the WGS84 meridian has nothing to do with the sun. The satellites have large solar panels - just think of WGS84 as being solar powered! Spin-off: the dials on the zero meridian UK, France and Spain. RM: precision with free apps. All very good, and I tried an experiment with my Axxera GPS receiver and two averaging apps (GPS Averaging and Perfect Mark) on my iPad. The Axxera quotes a CEP of ±2.5 metres, but the experiment was to see if I could determine a change in longitude by placing a *1 metre rule* aligned with the latitude in a open area on my lawn. As it happens, for my latitude (51º 22' N) 1 metre corresponds to 0.001 minute of arc in longitude. The systems update every second so it was no trouble to average 100 samples for 3 sets of readings for each averaging app. For the GPS Averaging I got 0º 48.1357' and 0º 48.1367' at either end of the rule, and for the Perfect Mark 0º 48.1362' and 0º 48.1377. In other words definitely resolving a metre on the ground. I expect that repeating for another 600 readings half an hour later (all different satellites and bearings) I may have obtained higher precision still by combining both sets of data. Amazing. Thanks again for the fascinating insights. Regards, Doug PS An image of Frank King and BSS member Ian Butson recording the event of 0º 0' 0". Note the Greenwich landmarks in the background. The Greenwich meridian passes to the left of the power station chimneys. On 30/04/2014 17:37, Douglas Bateman wrote: This is a new club consisting, so far, of two members: Frank King and myself. After the successful British Sundial Society conference, the Sunday morning was allocated to tours of the Greenwich Observatory. Quite independently, Frank and I had the intention of location the WGS84 meridian, some 90m east of the Greenwich brass strip. Frank had an eTrex tracker and an app on his mobile phone, and I had an Axxera GPS tracker linked to my iPad. The images, if the system will let them through, show 0º 0' 0". Anyone else willing to join this new exclusive club? Plenty of places to straddle the line between the north pole and the south pole. Doug (and Frank) --- https://lists.uni-koeln.de/mailman/listinfo/sundial --- https://lists.uni-koeln.de/mailman/listinfo/sundial
Re: GPS and sextants, it is not that bad
Michael, Tom, Bill, John, Fernando et al Look, horsemanship is still with us, same is with sailing under sail, sundials are still being designed and built, Mike can gut a deer, even steam engines are maintained and used. So sextant will not perish. Its reign held well over 200 years. In 90-ties of our century it still had to be used in certain areas of the globe not covered by Loran or Deca. It is still being used on many yachts, So it is not that bad. Sextants are still being produced and sold and not only as decorations. Sextant in its beginnings pushed into obscurity another marvelous device, that is astrolabe which was also amazing celestial computer, much more abstract than celestial globe. GPS does not have soul but its inventors feel warmly about it. The idea was incredible, theoretically simple but technologically very advanced and complex. As Mike noted satelites may be turned off or shot down and in such case come back of the sextant may be very fast. During WWII convoy navigators, whatever their civilian backgrounds, became superb sextant users. It was a must. Not only radio beacons were off but lighthouses as well, not to mention that convoy ships used light only for Morse code communication. Sextant does have a soul, as I mentioned it requires respect and devotion. The thrill when you see for the first time how fast the Sun moves in its view is incomparable. Certainly you touch the Universe, like with sundial. Slawek Slawek Grzechnik 32 57.4'N 117 08.8'W http://home.san.rr.com/slawek
Re: Time question on GPS TIME and leap second.
Yes. The navigation message transmitted by GPS satellites includes the current leap second offset so a receiver can compute and display correct UTC. -- Richard Langley Sent from my iPhone On Jan 29, 2017, at 6:05 PM, rodwall1...@gmail.com<mailto:rodwall1...@gmail.com> mailto:rodwall1...@gmail.com>> wrote: Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" mailto:email9648...@gmail.com>> To: "Robert Kellogg" mailto:rkell...@comcast.net>> Cc: "sundial list" mailto:sundial@uni-koeln.de>> Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg mailto:rkell...@comcast.net>> wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.24219 days, when it's really 365.24217 mean days long. ...for the purposes of a calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, and due to gradual change in the lengths of all the tropical years, including the MTY. But that doesn't mean we have to intentionally add avoidable error. > Contemplating decoupling UTC from the rotation of the earth (ie necessity > of being within .9 sec of UT1) likewise has significant consequences. > Let's let the IAU chart the future of time. Sure, but it isn't necessary to base a calendar on a day that isn't today's mean solar day. Michael Ossipoff > Dennis and Ken, if you're listening to this discussion, please chime in. > > > On 1/29/2017 12:27 PM, > sundial-requ...@uni-koeln.de<mailto:sundial-requ...@uni-koeln.de> wrote: > >> Send sundial mailing list submissions to >> sundial@uni-koeln.de<mailto:sundial@uni-koeln.de> >> >> To subscribe or unsubscribe via the World Wide Web, visit >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> or, via email, send a message with subject or body 'help' to >> sundial-requ...@uni-koeln.de<mailto:sundial-requ...@uni-koeln.de> >> >> You can reach the person managing the list at >> sundial-ow...@uni-koeln.de<mailto:sundial-ow...@uni-koeln.de> >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of sundial digest..." >> >> >> Today's Topics: >> >> 1. Re: Why we should reform the Calendar (Michael Ossipoff) >> >> >> -- >> >> Message: 1 >> Date: Sun, 29 Jan 2017 12:27:56 -0500 >> From: Michael Ossipoff >> mailto:email9648...@gmail.com>> >> To: Dan-George Uza mailto:cerculdest...@gmail.com>> >&
AW: Time question on GPS TIME and leap second.
Hello Rod, I just added a little MP4 video from the last leap second to my homepage. So you can see how it works. Look here: www.sonnenuhren-lindner.de <http://www.sonnenuhren-lindner.de> Regards. Peter Von: sundial [mailto:sundial-boun...@uni-koeln.de] Im Auftrag von Richard Langley Gesendet: Montag, 30. Januar 2017 00:02 An: rodwall1...@gmail.com Cc: sundial list Betreff: Re: Time question on GPS TIME and leap second. Yes. The navigation message transmitted by GPS satellites includes the current leap second offset so a receiver can compute and display correct UTC. -- Richard Langley Sent from my iPhone On Jan 29, 2017, at 6:05 PM, rodwall1...@gmail.com <mailto:rodwall1...@gmail.com> mailto:rodwall1...@gmail.com> > wrote: Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" mailto:email9648...@gmail.com> > To: "Robert Kellogg" mailto:rkell...@comcast.net> > Cc: "sundial list" mailto:sundial@uni-koeln.de> > Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg mailto:rkell...@comcast.net> > wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.24219 days, when it's really 365.24217 mean days long. ...for the purposes of a calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, and due to gradual change in the lengths of all the tropical years, including the MTY. But that doesn't mean we have to intentionally add avoidable error. > Contemplating decoupling UTC from the rotation of the earth (ie necessity > of being within .9 sec of UT1) likewise has significant consequences. > Let's let the IAU chart the future of time. Sure, but it isn't necessary to base a calendar on a day that isn't today's mean solar day. Michael Ossipoff > Dennis and Ken, if you're listening to this discussion, please chime in. > > > On 1/29/2017 12:27 PM, sundial-requ...@uni-koeln.de <mailto:sundial-requ...@uni-koeln.de> wrote: > >> Send sundial mailing list submissions to >> sundial@uni-koeln.de <mailto:sundial@uni-koeln.de> >> >> To subscribe or unsubscribe via the World Wide Web, visit >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> or, via email, send a message with subject or body 'help' to >> sundial-requ...@uni-koeln.de <mailto:sundial-requ...@uni-koeln.de> >> >> You can reach the person managing the list at >> sundial-ow...@uni-koeln.de <mailto:sundial-ow...@uni-koeln.de> >> >> When replying, please edit your Subject line so it is mor
Re: Time question on GPS TIME and leap second.
Here is a link to an old GPS World article on GPS and the leap second: http://www2.unb.ca/gge/Resources/gpsworld.november99.pdf See the "The GPS Navigation Message" sidebar in particular. And an article from GPS World on the occasion of the previous leap second: http://gpsworld.com/its-leap-second-day-time-to-get-in-sync/ -- Richard Langley - | Richard B. LangleyE-mail: l...@unb.ca | | Geodetic Research Laboratory Web: http://gge.unb.ca<http://gge.unb.ca/> | | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3| |Fredericton? Where's that? See: http://www.fredericton.ca/<https://unbmail.unb.ca/owa/redir.aspx?C=tVxi5OaRXE2jUmSNTu0wE7USusV6L9AIh-TKOqhq1DE--EjKeq-SUal8Myg-FGJn53Gm890SFIc.&URL=http%3a%2f%2fwww.fredericton.ca%2f> | - From: sundial on behalf of Richard Langley Sent: Sunday, January 29, 2017 7:02 PM To: rodwall1...@gmail.com Cc: sundial list Subject: Re: Time question on GPS TIME and leap second. Yes. The navigation message transmitted by GPS satellites includes the current leap second offset so a receiver can compute and display correct UTC. -- Richard Langley Sent from my iPhone On Jan 29, 2017, at 6:05 PM, rodwall1...@gmail.com<mailto:rodwall1...@gmail.com> mailto:rodwall1...@gmail.com>> wrote: Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" mailto:email9648...@gmail.com>> To: "Robert Kellogg" mailto:rkell...@comcast.net>> Cc: "sundial list" mailto:sundial@uni-koeln.de>> Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg mailto:rkell...@comcast.net>> wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.24219 days, when it's really 365.24217 mean days long. ...for the purposes of a calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, and due to gradual change in the lengths of all the tropical years, including the MTY. But that doesn't mean we have to intentionally add avoidable error. > Contemplating decoupling UTC from the rotation of the earth (ie necessity > of being within .9 sec of UT1) likewise has significant consequences. > Let's let the IAU chart the future of time. Sure, but it isn't necessary to base a calendar on a day that isn't today's mean solar day. Michael Ossipoff
Re: Time question on GPS TIME and leap second.
Hi Roderick: GPS time is continuous, that's to say there are no leap seconds or other changes to it since it started. It uses a 10 bit binary week counter so the week number rolls over after 1024 weeks. This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is. The total number of seconds offset from UTC is transmitted separately so that a GPS receiver can display either GPS time or UTC. Note that the time and position are independent from the year. http://www.prc68.com/I/Trimpack.shtml#WkRlvr -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" To: "Robert Kellogg" Cc: "sundial list" Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.24219 days, when it's really 365.24217 mean days long. ...for the purposes of a calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, and due to gradual change in the lengths of all the tropical years, including the MTY. But that doesn't mean we have to intentionally add avoidable error. > Contemplating decoupling UTC from the rotation of the earth (ie necessity > of being within .9 sec of UT1) likewise has significant consequences. > Let's let the IAU chart the future of time. Sure, but it isn't necessary to base a calendar on a day that isn't today's mean solar day. Michael Ossipoff > Dennis and Ken, if you're listening to this discussion, please chime in. > > > On 1/29/2017 12:27 PM, sundial-requ...@uni-koeln.de wrote: > >> Send sundial mailing list submissions to >> sundial@uni-koeln.de >> >> To subscribe or unsubscribe via the World Wide Web, visit >>https://lists.uni-koeln.de/mailman/listinfo/sundial >> or, via email, send a message with subject or body 'help' to >> sundial-requ...@uni-koeln.de >> >> You can reach the person managing the list at >> sundial-ow...@uni-koeln.de >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of sundial digest..." >> >> >> Today's Topics: >> >> 1. Re: Why we should reform the Calendar (Michael Ossipoff) >> >> >> -- >> >> Message: 1 >> Date: Sun, 29 Jan 2017 12:27:56 -0500 >> From: Michael Ossipoff >> To: Dan-George Uza >> Cc: sundial list >
Re: Time question on GPS TIME and leap second.
"This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is." Not quite true. One of the continuously operating receivers at UNB is more than 15 years old. Please see: http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf -- Richard Langley - | Richard B. LangleyE-mail: l...@unb.ca | | Geodetic Research Laboratory Web: http://gge.unb.ca<http://gge.unb.ca/> | | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3| |Fredericton? Where's that? See: http://www.fredericton.ca/<https://unbmail.unb.ca/owa/redir.aspx?C=tVxi5OaRXE2jUmSNTu0wE7USusV6L9AIh-TKOqhq1DE--EjKeq-SUal8Myg-FGJn53Gm890SFIc.&URL=http%3a%2f%2fwww.fredericton.ca%2f> | - From: sundial on behalf of Brooke Clarke Sent: Monday, January 30, 2017 4:29 PM To: sundial list Subject: Re: Time question on GPS TIME and leap second. Hi Roderick: GPS time is continuous, that's to say there are no leap seconds or other changes to it since it started. It uses a 10 bit binary week counter so the week number rolls over after 1024 weeks. This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is. The total number of seconds offset from UTC is transmitted separately so that a GPS receiver can display either GPS time or UTC. Note that the time and position are independent from the year. http://www.prc68.com/I/Trimpack.shtml#WkRlvr -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" <mailto:email9648...@gmail.com> To: "Robert Kellogg" <mailto:rkell...@comcast.net> Cc: "sundial list" <mailto:sundial@uni-koeln.de> Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg <mailto:rkell...@comcast.net> wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.24219 days, when it's really 365.24217 mean days long. ...for the purposes of a calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, and due to gradual change in the lengths of all the tropical years, including the MTY. But that doesn't mean we have to intentionally add avoidable error. > Contemplating dec
Re: Time question on GPS TIME and leap second.
Thanks to all who replied to my questions about the time on GPS. The reason I asked about the leap second. Is if the following analog clock GPS driver included the leap second correction. Yes it would. http://www.altronics.com.au/p/k1129-gps-synchronised-clock-kit/ It also corrects it for daylight saving. Thanks all, Roderick Wall. - Reply message - From: "Brooke Clarke" To: "sundial list" Subject: Time question on GPS TIME and leap second. Date: Tue, Jan 31, 2017 7:29 AM Hi Roderick: GPS time is continuous, that's to say there are no leap seconds or other changes to it since it started. It uses a 10 bit binary week counter so the week number rolls over after 1024 weeks. This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is. The total number of seconds offset from UTC is transmitted separately so that a GPS receiver can display either GPS time or UTC. Note that the time and position are independent from the year. http://www.prc68.com/I/Trimpack.shtml#WkRlvr -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message > Hi all, > > Was just listening to the CrowdScience on time. Thanks to whoever posted the > link to it. > > CrowdScience indicated that a leap second was not added for the GPS. They > also indicated that the GPS gives us UTC time. > > Question: > The UTC time that the GPS gives. Does that have the leap second added? > > Thanks, > > Regards, > > Roderick Wall. > > - Reply message - > From: "Michael Ossipoff" > To: "Robert Kellogg" > Cc: "sundial list" > Subject: Why we should reform the Calendar > Date: Mon, Jan 30, 2017 8:00 AM > > On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg > wrote: > > > Michael goes off looking for the ideal tropical year > > > There isn't an "ideal tropical year", but, as a choice for a > leapyear-rule's mean-year, the length of the mean tropical year (MTY) is > best for year-round reduction of longterm calendar-drift. ...and the > average of the lengths of the March & September Equinox tropical years > (I'll call that the Average Equinox Year (AEY) ) is a compromise between > the vernal equinoxes of the North & the South. > > > > , perhaps ignoring effects of the earth's nutations. > > > > Of course. The nutations are small in amplitude & period. They aren't part > of calendar rules. The mean equinox (nutations averaged-out) is the one > that is meant when the equinox is spoken of with regard to calendars. > > > > > I'll still take the one of 1900, most importantly because it defines the > > SI second. > > > The SI second was defined as 1/86,400 of a mean solar day, for some year in > the early 19th century. I don't remember exactly what year that was. 1820? > 1840? 1850? > > Evidently it isn't practical to update the length of the SI second, but > that doesn't mean that calendars have to be based on the ephemeris day, or > atomic day, consisting of 86,400 SI seconds, when that's known to be > different from today's mean solar day. > > That's why I suggest 365.24217 instead of 365.24219 for the length of the > mean tropical year (MTYI. It makes sense to base a calendar leap-year > rule's mean-year on the actual length of a tropical-year (whichever one we > want to use) on the length of that tropical year in* today's* mean days. > > > > > > > > So, contemplating changing the year is non trivial. > > > Evidently there must be some reason why it would be impractical to update > the length of the SI second. But it isn't necessary to call a MTY 365.24219 > days, when it's really 365.24217 mean days long. ...for the purposes of a > calendar leapyear rule. There's inevitable inaccuracy due to rounding-off, > and due to gradual change in the lengths of all the tropical years, > including the MTY. But that doesn't mean we have to intentionally add > avoidable error. > > > > > Contemplating decoupling UTC from the rotation of the earth (ie necessity > > of being within .9 sec of UT1) likewise has significant consequences. > > Let's let the IAU chart the future of time. > > > Sure, but it isn't necessary to base a calendar on a day that isn't today's > mean solar day. > > Michael Ossipoff > > > > > > > Dennis and Ken, if you're listening to this discussion, please chime in. > > > > > > On 1/29/2017 12:27 PM, sundial-requ...@uni-koeln.de wrote: > > > >> Send su
Re: Time question on GPS TIME and leap second.
A recent article on the GPS analog clock driver. A better description; http://archive.siliconchip.com.au/cms/A_92/article.html Roderick Wall. - Reply message - From: "Richard Langley" To: "Brooke Clarke" , "sundial list" Subject: Time question on GPS TIME and leap second. Date: Tue, Jan 31, 2017 10:33 AM "This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is." Not quite true. One of the continuously operating receivers at UNB is more than 15 years old. Please see: http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf -- Richard Langley - | Richard B. LangleyE-mail: l...@unb.ca | | Geodetic Research Laboratory Web: http://gge.unb.ca<http://gge.unb.ca/> | | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3| |Fredericton? Where's that? See: http://www.fredericton.ca/<https://unbmail.unb.ca/owa/redir.aspx?C=tVxi5OaRXE2jUmSNTu0wE7USusV6L9AIh-TKOqhq1DE--EjKeq-SUal8Myg-FGJn53Gm890SFIc.&URL=http%3a%2f%2fwww.fredericton.ca%2f> | - From: sundial on behalf of Brooke Clarke Sent: Monday, January 30, 2017 4:29 PM To: sundial list Subject: Re: Time question on GPS TIME and leap second. Hi Roderick: GPS time is continuous, that's to say there are no leap seconds or other changes to it since it started. It uses a 10 bit binary week counter so the week number rolls over after 1024 weeks. This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is. The total number of seconds offset from UTC is transmitted separately so that a GPS receiver can display either GPS time or UTC. Note that the time and position are independent from the year. http://www.prc68.com/I/Trimpack.shtml#WkRlvr -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" <mailto:email9648...@gmail.com> To: "Robert Kellogg" <mailto:rkell...@comcast.net> Cc: "sundial list" <mailto:sundial@uni-koeln.de> Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg <mailto:rkell...@comcast.net> wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemeris day, or atomic day, consisting of 86,400 SI seconds, when that's known to be different from today's mean solar day. That's why I suggest 365.24217 instead of 365.24219 for the length of the mean tropical year (MTYI. It makes sense to base a calendar leap-year rule's mean-year on the actual length of a tropical-year (whichever one we want to use) on the length of that tropical year in* today's* mean days. > > > So, contemplating changing the year is non trivial. Evidently there must be some reason why it would be impractical to update the length of the SI second. But it isn't necessary to call a MTY 365.2
Re: Time question on GPS TIME and leap second.
Hi Roderick: GPS knows about neither daylight savings nor the date. The article mentions "understands the rules of daylight saving (DST)" which are a political thing so this will only work until the rules change. This happened to VCR players and after the rules change they are always wrong. The only time source that knows about these things are the time stations, like WWV & WWVB. http://www.prc68.com/I/timefreq.shtml#RSL -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message A recent article on the GPS analog clock driver. A better description; http://archive.siliconchip.com.au/cms/A_92/article.html Roderick Wall. - Reply message - From: "Richard Langley" To: "Brooke Clarke" , "sundial list" Subject: Time question on GPS TIME and leap second. Date: Tue, Jan 31, 2017 10:33 AM "This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is." Not quite true. One of the continuously operating receivers at UNB is more than 15 years old. Please see: http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf <http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf%E2%80%8B> -- Richard Langley - | Richard B. LangleyE-mail: l...@unb.ca | | Geodetic Research Laboratory Web:http://gge.unb.ca<http://gge.unb.ca/> | | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | | University of New Brunswick Fax: +1 506 453-4943 | | Fredericton, N.B., Canada E3B 5A3| |Fredericton? Where's that? See:http://www.fredericton.ca/<https://unbmail.unb.ca/owa/redir.aspx?C=tVxi5OaRXE2jUmSNTu0wE7USusV6L9AIh-TKOqhq1DE--EjKeq-SUal8Myg-FGJn53Gm890SFIc.&URL=http%3a%2f%2fwww.fredericton.ca%2f> | - From: sundial on behalf of Brooke Clarke Sent: Monday, January 30, 2017 4:29 PM To: sundial list Subject: Re: Time question on GPS TIME and leap second. Hi Roderick: GPS time is continuous, that's to say there are no leap seconds or other changes to it since it started. It uses a 10 bit binary week counter so the week number rolls over after 1024 weeks. This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is. The total number of seconds offset from UTC is transmitted separately so that a GPS receiver can display either GPS time or UTC. Note that the time and position are independent from the year. http://www.prc68.com/I/Trimpack.shtml#WkRlvr -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message Hi all, Was just listening to the CrowdScience on time. Thanks to whoever posted the link to it. CrowdScience indicated that a leap second was not added for the GPS. They also indicated that the GPS gives us UTC time. Question: The UTC time that the GPS gives. Does that have the leap second added? Thanks, Regards, Roderick Wall. - Reply message - From: "Michael Ossipoff" <mailto:email9648...@gmail.com> To: "Robert Kellogg" <mailto:rkell...@comcast.net> Cc: "sundial list" <mailto:sundial@uni-koeln.de> Subject: Why we should reform the Calendar Date: Mon, Jan 30, 2017 8:00 AM On Sun, Jan 29, 2017 at 2:41 PM, Robert Kellogg <mailto:rkell...@comcast.net> wrote: > Michael goes off looking for the ideal tropical year There isn't an "ideal tropical year", but, as a choice for a leapyear-rule's mean-year, the length of the mean tropical year (MTY) is best for year-round reduction of longterm calendar-drift. ...and the average of the lengths of the March & September Equinox tropical years (I'll call that the Average Equinox Year (AEY) ) is a compromise between the vernal equinoxes of the North & the South. > , perhaps ignoring effects of the earth's nutations. > Of course. The nutations are small in amplitude & period. They aren't part of calendar rules. The mean equinox (nutations averaged-out) is the one that is meant when the equinox is spoken of with regard to calendars. > I'll still take the one of 1900, most importantly because it defines the > SI second. The SI second was defined as 1/86,400 of a mean solar day, for some year in the early 19th century. I don't remember exactly what year that was. 1820? 1840? 1850? Evidently it isn't practical to update the length of the SI second, but that doesn't mean that calendars have to be based on the ephemer
Re: Time question on GPS TIME and leap second.
Hi Brooke, True, GPS doesn't know about daylight saving. To set the clock up after building it. You use a RS232 Com terminal program, to talk to the clock driver microprocessor. And set up the month and which Sunday daylight saving starts and finishes. You need to: Set your time zone. Daylight saving ON or OFF. Start daylight saving month. Start daylight saving Sunday. End daylight saving month. End daylight saving Sunday. Set clock pulse mSeconds. Set GPS update (hours). Q = quit. Command:_ The firmware is written in the C language. Source code can be downloaded and you can play around with it if you want. Article also gives a web link for the free Hi-Tech C Compiler. I'm waiting to see if a local electronic supplier produces a kit of parts for it. Looks like fun, Roderick Wall. - Reply message - From: "Brooke Clarke" To: "sundial list" Subject: Time question on GPS TIME and leap second. Date: Thu, Feb 2, 2017 9:26 AM Hi Roderick: GPS knows about neither daylight savings nor the date. The article mentions "understands the rules of daylight saving (DST)" which are a political thing so this will only work until the rules change. This happened to VCR players and after the rules change they are always wrong. The only time source that knows about these things are the time stations, like WWV & WWVB. http://www.prc68.com/I/timefreq.shtml#RSL -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message > A recent article on the GPS analog clock driver. A better description; > > http://archive.siliconchip.com.au/cms/A_92/article.html > > Roderick Wall. > > - Reply message - > From: "Richard Langley" > To: "Brooke Clarke" , "sundial list" > > Subject: Time question on GPS TIME and leap second. > Date: Tue, Jan 31, 2017 10:33 AM > > "This causes problems for GPS receivers that are more than a few years old > since they have no idea what year it is." > > > Not quite true. One of the continuously operating receivers at UNB is more > than 15 years old. Please see: > > http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf > <http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf%E2%80%8B> > > > -- Richard Langley > > > - > | Richard B. LangleyE-mail: l...@unb.ca | > | Geodetic Research Laboratory > Web:http://gge.unb.ca<http://gge.unb.ca/> | > | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | > | University of New Brunswick Fax: +1 506 453-4943 | > | Fredericton, N.B., Canada E3B 5A3| > |Fredericton? Where's that? > See:http://www.fredericton.ca/<https://unbmail.unb.ca/owa/redir.aspx?C=tVxi5OaRXE2jUmSNTu0wE7USusV6L9AIh-TKOqhq1DE--EjKeq-SUal8Myg-FGJn53Gm890SFIc.&URL=http%3a%2f%2fwww.fredericton.ca%2f> >| > ----- > > From: sundial on behalf of Brooke Clarke > > Sent: Monday, January 30, 2017 4:29 PM > To: sundial list > Subject: Re: Time question on GPS TIME and leap second. > > Hi Roderick: > > GPS time is continuous, that's to say there are no leap seconds or other > changes to it since it started. It uses a 10 bit binary week counter so the > week number rolls over after 1024 weeks. This causes problems for GPS > receivers that are more than a few years old since they have no idea what > year it is. > The total number of seconds offset from UTC is transmitted separately so that > a GPS receiver can display either GPS time or UTC. > Note that the time and position are independent from the year. > > http://www.prc68.com/I/Trimpack.shtml#WkRlvr > > -- > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > > > Original Message > Hi all, > > Was just listening to the CrowdScience on time. Thanks to whoever posted the > link to it. > > CrowdScience indicated that a leap second was not added for the GPS. They > also indicated that the GPS gives us UTC time. > > Question: > The UTC time that the GPS gives. Does that have the leap second added? > > Thanks, > > Regards, > > Roderick Wall. > > - Reply message - > From: "Michael Ossipoff" > <mailto:email9648...@gmail.com> > To: "Robert Kellogg" <mailto:rkell...@comcast.net> > Cc: "sundial list" &l
Re: Time question on GPS TIME and leap second.
Hi Rod: OK, that allows you to set the clock., but it's not a stand alone self setting clock. I was disappointed with the Heathkit GC-1000 when I found that it was off by an hour at the changes of daylight savings in displaying my local time. (It changed time when the transmitter in Colorado changed it's time rather than when it should.) As far as I know that was never fixed. GPS does not know about the date or daylight savings, but does have a way to get to UTC by using the accumulated offset between GPS and UTC. So the only way to have an accurate and self setting clock is to make use of a "time" station like WWV or WWVB. I've only heard of one clock model that makes use of the phase modulation that's been on WWVB for many years and it's the La Crosse 404-1235UA-SS. -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message Hi Brooke, True, GPS doesn't know about daylight saving. To set the clock up after building it. You use a RS232 Com terminal program, to talk to the clock driver microprocessor. And set up the month and which Sunday daylight saving starts and finishes. You need to: Set your time zone. Daylight saving ON or OFF. Start daylight saving month. Start daylight saving Sunday. End daylight saving month. End daylight saving Sunday. Set clock pulse mSeconds. Set GPS update (hours). Q = quit. Command:_ The firmware is written in the C language. Source code can be downloaded and you can play around with it if you want. Article also gives a web link for the free Hi-Tech C Compiler. I'm waiting to see if a local electronic supplier produces a kit of parts for it. Looks like fun, Roderick Wall. - Reply message - From: "Brooke Clarke" To: "sundial list" Subject: Time question on GPS TIME and leap second. Date: Thu, Feb 2, 2017 9:26 AM Hi Roderick: GPS knows about neither daylight savings nor the date. The article mentions "understands the rules of daylight saving (DST)" which are a political thing so this will only work until the rules change. This happened to VCR players and after the rules change they are always wrong. The only time source that knows about these things are the time stations, like WWV & WWVB. http://www.prc68.com/I/timefreq.shtml#RSL -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message > A recent article on the GPS analog clock driver. A better description; > >http://archive.siliconchip.com.au/cms/A_92/article.html > > Roderick Wall. > > - Reply message ----- > From: "Richard Langley" > To: "Brooke Clarke" , "sundial list" > Subject: Time question on GPS TIME and leap second. > Date: Tue, Jan 31, 2017 10:33 AM > > "This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is." > > > Not quite true. One of the continuously operating receivers at UNB is more than 15 years old. Please see: > >http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf <http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf%E2%80%8B> > <http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf%E2%80%8B> > > > -- Richard Langley > > > - > | Richard B. LangleyE-mail: l...@unb.ca | > | Geodetic Research Laboratory Web:http://gge.unb.ca<http://gge.unb.ca/> | > | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 | > | University of New Brunswick Fax: +1 506 453-4943 | > | Fredericton, N.B., Canada E3B 5A3| > |Fredericton? Where's that? See:http://www.fredericton.ca/<https://unbmail.unb.ca/owa/redir.aspx?C=tVxi5OaRXE2jUmSNTu0wE7USusV6L9AIh-TKOqhq1DE--EjKeq-SUal8Myg-FGJn53Gm890SFIc.&URL=http%3a%2f%2fwww.fredericton.ca%2f> | > --------- > > From: sundial on behalf of Brooke Clarke > Sent: Monday, January 30, 2017 4:29 PM > To: sundial list > Subject: Re: Time question on GPS TIME and leap second. > > Hi Roderick: > > GPS time is continuous, that's to say there are no leap seconds or other changes to it since it started. It uses a 10 bit binary week counter so the week number rolls over after 1024 weeks. This causes problems for GPS receivers that are more than a few years old since they have no idea what year it is. > The total number of seconds offset from UTC is transmitted separately so that a GPS receiver
Re: Time question on GPS TIME and leap second.
Hi Brooke, The radio controlled clock that you described that uses WWVB is very good. If you live in Canada, America or Mexico. But I don't think it would work in Australia or some other parts in the world. Where the GPS signals can be received anywhere. For the Silicon Chip GPS controlled clock. The firmware is written in the C programming language. And is available if you want to make it work the way you want it to. Have fun, Roderick Wall. - Reply message - From: "Brooke Clarke" To: "rodwall1...@gmail.com" , "sundial list" Subject: Time question on GPS TIME and leap second. Date: Fri, Feb 3, 2017 6:06 AM Hi Rod: OK, that allows you to set the clock., but it's not a stand alone self setting clock. I was disappointed with the Heathkit GC-1000 when I found that it was off by an hour at the changes of daylight savings in displaying my local time. (It changed time when the transmitter in Colorado changed it's time rather than when it should.) As far as I know that was never fixed. GPS does not know about the date or daylight savings, but does have a way to get to UTC by using the accumulated offset between GPS and UTC. So the only way to have an accurate and self setting clock is to make use of a "time" station like WWV or WWVB. I've only heard of one clock model that makes use of the phase modulation that's been on WWVB for many years and it's the La Crosse 404-1235UA-SS. -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message > Hi Brooke, > > True, GPS doesn't know about daylight saving. > > To set the clock up after building it. You use a RS232 Com terminal program, > to talk to the clock driver > microprocessor. And set up the month and which Sunday daylight saving starts > and finishes. > > You need to: > Set your time zone. > Daylight saving ON or OFF. > Start daylight saving month. > Start daylight saving Sunday. > End daylight saving month. > End daylight saving Sunday. > Set clock pulse mSeconds. > Set GPS update (hours). > > Q = quit. > > Command:_ > > The firmware is written in the C language. Source code can be downloaded and > you can play around with it if you want. > > Article also gives a web link for the free Hi-Tech C Compiler. > > I'm waiting to see if a local electronic supplier produces a kit of parts for > it. > > Looks like fun, > > Roderick Wall. > > - Reply message - > From: "Brooke Clarke" > To: "sundial list" > Subject: Time question on GPS TIME and leap second. > Date: Thu, Feb 2, 2017 9:26 AM > > Hi Roderick: > > GPS knows about neither daylight savings nor the date. > The article mentions "understands the rules of daylight saving (DST)" which > are a political thing so this will only work > until the rules change. > This happened to VCR players and after the rules change they are always wrong. > The only time source that knows about these things are the time stations, > like WWV & WWVB. > http://www.prc68.com/I/timefreq.shtml#RSL > > -- > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > > Original Message > > A recent article on the GPS analog clock driver. A better description; > > > >http://archive.siliconchip.com.au/cms/A_92/article.html > > > > Roderick Wall. > > > > - Reply message - > > From: "Richard Langley" > > To: "Brooke Clarke" , "sundial list" > > > > Subject: Time question on GPS TIME and leap second. > > Date: Tue, Jan 31, 2017 10:33 AM > > > > "This causes problems for GPS receivers that are more than a few years old > > since they have no idea what year it is." > > > > > > Not quite true. One of the continuously operating receivers at UNB is more > > than 15 years old. Please see: > > > >http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf > <http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf%E2%80%8B> > > <http://gauss2.gge.unb.ca/gpsworld/gpsworld.november98.pdf%E2%80%8B> > > > > > > -- Richard Langley > > > > > > - > > | Richard B. LangleyE-mail: l...@unb.ca > > | > > | Geodetic Research Laboratory > > Web:http://gge.unb.ca<http://gge.unb.ca/> | > > | Dept. of Geodesy and Geomatics EngineeringPhone:+1 506 453-5142 > > |
Re: Time question on GPS TIME and leap second.
While I am truly fond of analog clocks, certainly including sundials, I also have a place in my heart for interesting digital clocks. Hence, I still have two Heathkit "Most Accurate Clocks," model GC-1000, that run 24/7 and have done for 30 years. This red LED digital clock sets its time from WWV (not WWVB) using the two-tone, seconds-tick tone; that seconds-tick tone digitally encodes the time of day, DST and more. The Heath clock decodes it, displaying hours, minutes, seconds and tenths of seconds. For its era, this Heath clock has many innovative features, including learning and correcting the frequency error of its internal crystal. Originally a relatively expensive Heathkit product selling for about $250, it now sells for $400-$600 on eBay! Bet you did not know the WWV seconds-tick tone actually shifts between two different tones to allow this encoding! No, I can't hear the difference. But, that was before GPS time. I recently found a kit for a red LED digital clock that uses GPS and displays hours, minutes, seconds and also tenths of seconds. Try that with a sundial! Of course, you don't need to plug in your sundial... Look here for the $60 GPS Clock: https://www.tindie.com/products/nsayer/gps-clock/ I've had one of these GPS Clocks running for about a month and it has been absolutely reliable, syncing quickly to GPS upon power-up from a 5 volt wall wart power supply. Larry On 1/31/2017 11:46 PM, rodwall1...@gmail.com wrote: A recent article on the GPS analog clock driver. A better description; http://archive.siliconchip.com.au/cms/A_92/article.html Roderick Wall. ... -- Best wishes, Larry McDavid W6FUB Anaheim, California (SE of Los Angeles, near Disneyland) --- https://lists.uni-koeln.de/mailman/listinfo/sundial
