Re: [time-nuts] nuts about position
I would be quite interested in the results of this test from something like a Ublox 6T or 8 unit. Please keep us posted. Dan On 6/5/2018 2:35 PM, time-nuts-requ...@febo.com wrote: The next thing I want to try is a receiver self-survey vs the post processed results... I may be able to kludge up a test that does a self-survey / precision survey / post processed survey and compare the results of the methods on the same data set. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
In message , Mark Sims writes: >The effects of things like antenna position changing a couple of cm due to >expansion and humidity effects are swamped by the receiver accuracy and noise. Short term: Yes. Long term: No. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
The typical receiver default self-surveys of 30 minutes to 2 hours are not ideal. They will not include a lot of satellites or the effects of multi-path over time. A survey of at least 12 hours is needed to include all the sats. 24-48 hours is even better. The effects of things like antenna position changing a couple of cm due to expansion and humidity effects are swamped by the receiver accuracy and noise. - > That said, there are certainly a lot of issues with how the self-survey position should be calculated *and* maintained, because it really needs to change over time for optimal performance. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
In message , Mark Sims writes: >The next thing I want to try is a receiver self-survey vs the post processed >results... I fell into that trap many years ago as well :-) The post processed result eliminates and compensates for a lot of effects which are invisible to the receiver, that is the entire point of post processing. But if your goal is to get good 1PPS out of your receiver, forcing it to hold a "perfect" position, means asking it to deal with effects it cannot measure, and as a result you get *worse* 1PPS performance than if you use the "wrong" self-survey position. That said, there are certainly a lot of issues with how the self-survey position should be calculated *and* maintained, because it really needs to change over time for optimal performance. Almost any suboptimal antenna-position means that you should vary the position-hold coordinates over the orbital period (but see below), but over longer periods also environmental factors come into play. For instance if you put the antenna on a wood-construction, be it a pole or a house, it coordinates will vary at the cm level over the seasons as the wood expands and contracts. The good news is that the receiver gives you the input data to work and model these biases, the bad news you don't get a lot of data. I did some experiments when ten Oncore M12+T's passed through my lab many years ago: I plotted the reported "residuals" vs. satellite position, and I tried to update the held position on a daily basis using the trend, and the results were measurable at the several ns level: http://phk.freebsd.dk/raga/sneak/ I didn't persue this further, because my latitude is particular unfavourable to the simple (N/S+E/W) approach (no birds north of me) and with only a single receiver the amount of input data is too low for such a crude algorithm. A more complex geometrical model could probably get more mileage out of the sparse data, as would tracking more birds than the 12 the M12 could track. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
The tripod is a survey grade tripod on a limestone terrace (in a horrible location for an antenna). Heather's precision survey uses the receiver's reported position data. It does not take advantage of carrier phase/pseduorange/doppler data and post-processing. Unlike the simple averaging self-surveys that most receivers do it processes the average of medians over 1 minute/1 hour/24 hour intervals. It typically produces results 1-2m better than the simple self-surveys. The next thing I want to try is a receiver self-survey vs the post processed results... I may be able to kludge up a test that does a self-survey / precision survey / post processed survey and compare the results of the methods on the same data set. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi Hmmm …… that’s a very big difference between the RINEX and the “precision survey”. How do each compare to other receivers on the same antenna ( and super duper stable mount) ? Even with a tripod on the grass, meter level variations likely are not the tripod’s fault. :) Bob > On Jun 5, 2018, at 1:39 PM, Mark Sims wrote: > > I did Lady Heather's 48-hour precision survey on an NVS-08 receiver and > collected RINEX data at the same time. The NVS was tracking GPS and SBAS > satellites. > > The RINEX result had lat/lon/alt error estimates of .175/.153/.396 meters. > > The difference between Heather's precision survey results and the RINEX > position were: > lat/lon/alt: -.638m/1.190m/1.526m > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I did Lady Heather's 48-hour precision survey on an NVS-08 receiver and collected RINEX data at the same time. The NVS was tracking GPS and SBAS satellites. The RINEX result had lat/lon/alt error estimates of .175/.153/.396 meters. The difference between Heather's precision survey results and the RINEX position were: lat/lon/alt: -.638m/1.190m/1.526m ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi > On Jun 3, 2018, at 7:35 PM, Mark Sims wrote: > > As far as I'm concerned anything that you can do to improve the position > accuracy, environmental changes, noise environment, etc is a good thing. > Minimizing errors and disturbances can't hurt and may even improve things. > How much any improvement provides ... ??? But time nuts tend to be a bit > nutty about minimizing our therbligs ;-) > > Most receiver self-surveys seem to get your lat/lon to the 2-3 meter range. > Heather's median survey is in the 1-2 meter range. PPP data is in the < 0.25 > meter range... seems like something worthwhile. (altitude errors are usually > around twice the lat/lon error). > > There is always the possibility that some receiver model's computation of > lat/lon/alt could have some intrinsic bias in it. If so, a position > calculated by an external source could possibly degrade performance... If you go back to the NIST papers where they were testing timing modules, they indeed did find “gotcha’s” with putting in survey based coordinates. I don’t think they ever did PPP on the modules they published data on. Bob > > > >> Is this applicable to a Thunderbolt, and would this improved position > accuracy be expected to improve the time accuracy from a Thunderbolt > compared to using the older Lady Heather 24 hour self survey method? > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
As far as I'm concerned anything that you can do to improve the position accuracy, environmental changes, noise environment, etc is a good thing. Minimizing errors and disturbances can't hurt and may even improve things. How much any improvement provides ... ??? But time nuts tend to be a bit nutty about minimizing our therbligs ;-) Most receiver self-surveys seem to get your lat/lon to the 2-3 meter range. Heather's median survey is in the 1-2 meter range. PPP data is in the < 0.25 meter range... seems like something worthwhile. (altitude errors are usually around twice the lat/lon error). There is always the possibility that some receiver model's computation of lat/lon/alt could have some intrinsic bias in it. If so, a position calculated by an external source could possibly degrade performance... > Is this applicable to a Thunderbolt, and would this improved position accuracy be expected to improve the time accuracy from a Thunderbolt compared to using the older Lady Heather 24 hour self survey method? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi Location will always impact things a bit. At some point it does become a minor contributor. What point that is varies with a lot of things. One of them is indeed the propagation path to the satellites. How much the ionosphere and troposphere mess things up is very much a “that depends” sort of thing. There are corrections applied to the data as part of normal GPS L! operation. The degree to which these corrections work depends on how close things are to the “normal model”. That in turn depends to some degree on how active the sunspot cycle is at the time. Right now we are in a period of relatively low activity. That equates to the models mostly fitting better most of the time. If solar activity was somewhat higher, then things get more dynamic. The magic models and the broadcast data can’t keep up as well. That translates to more noise on the estimates and worse timing ( as well as an impact on location). Bob > On Jun 3, 2018, at 4:07 PM, Chris Caudle wrote: > > On Sun, June 3, 2018 12:57 am, Mark Sims wrote: >> Well, with a little prodding and help from Magnus, I now have the >> Trimble devices outputting RINEX files. > > Is this applicable to a Thunderbolt, and would this improved position > accuracy be expected to improve the time accuracy from a Thunderbolt > compared to using the older Lady Heather 24 hour self survey method? Or > is ionospheric noise the limiting factor so determining more accurate > position doesn't really help? > > -- > Chris Caudle > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi, On 06/03/2018 10:07 PM, Chris Caudle wrote: > On Sun, June 3, 2018 12:57 am, Mark Sims wrote: >> Well, with a little prodding and help from Magnus, I now have the >> Trimble devices outputting RINEX files. > > Is this applicable to a Thunderbolt, and would this improved position > accuracy be expected to improve the time accuracy from a Thunderbolt > compared to using the older Lady Heather 24 hour self survey method? Or > is ionospheric noise the limiting factor so determining more accurate > position doesn't really help? > Actual ionospheric and corrections isn't matching up too well, so this can be a way to achieve a better fixed location. Exactly how the Thunderbolt uses the data in its steering I don't know, it would be interesting to figure that out. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On Sun, June 3, 2018 12:57 am, Mark Sims wrote: > Well, with a little prodding and help from Magnus, I now have the > Trimble devices outputting RINEX files. Is this applicable to a Thunderbolt, and would this improved position accuracy be expected to improve the time accuracy from a Thunderbolt compared to using the older Lady Heather 24 hour self survey method? Or is ionospheric noise the limiting factor so determining more accurate position doesn't really help? -- Chris Caudle ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I did a test on a 1 second vs a stripped out 10 second rate from the same 24 hour run. The differences were down in the noise. Some people have actually reported slightly better results with 30 second vs 1 second data... but I doubt that... I suspect they used different data sets and the differences were just due to different data. --- If you are doing a longer run into one of the data analysis services - it does not seem to matter much what the spacing on the readings is ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi If you are doing a longer run into one of the data analysis services - it does not seem to matter much what the spacing on the readings is. One second data does not seem to produce any better result than 30 second data. I don’t think that the 3 second rate on the Trimble will have much impact on a 24 hour data set. Bob > On Jun 3, 2018, at 1:57 AM, Mark Sims wrote: > > Well, with a little prodding and help from Magnus, I now have the Trimble > devices outputting RINEX files. They have pseudorange, doppler, and signal > strength observations. A 5 hour 1Hz run was sent to CSRS-PPP and the > lat/lon/alt error ellipses were in the 250/250/700 mm range... that should > improve with a longer run. > > Firmware issues in the original Resolution-T limit those to a 3 second > observation rate. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I haven't done any extensive testing of how accurate the results are, but comparing them to the position produced by a L1/L2 (error ellipses < 50mm) they seem to be correct. One issue to be aware of is that some receivers want altitude in othometric height (MSL) and others use geoid (GPS) height. If you are transferring the PPP results to a receiver you need to watch out for what the receiver wants. Also MSL based receivers may be using different orthometric models, so knowing how to convert GPS height to what the receiver uses can be problematic. - > Does the position agree with other chip sets? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
hol...@hotmail.com said: > A 5 hour 1Hz run was sent to CSRS-PPP and the lat/lon/alt error ellipses > were in the 250/250/700 mm range... Does the position agree with other chip sets? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi, It would be nice to have direct access to the carrier-phase, but to rebuild that from doppler takes some care. Doing a mock phase-setup is trivial, but one then have the full noise of the code-phase, as well as double ionspheric offset to overcome, so that is not the best starting point. This is not just integger ambiguity, you really do not have a phase point to start at, but just changes in phase. Anyway, I am happy I could contribute some ideas and also some code, and that it works out. Being able to produce RINEX files and post-process them for better accuracy or whatever should be a great improvement, so it is worth a bit of effort. Also, it's a great learning tool. Cheers, Magnus On 06/03/2018 07:57 AM, Mark Sims wrote: > Well, with a little prodding and help from Magnus, I now have the Trimble > devices outputting RINEX files. They have pseudorange, doppler, and signal > strength observations. A 5 hour 1Hz run was sent to CSRS-PPP and the > lat/lon/alt error ellipses were in the 250/250/700 mm range... that should > improve with a longer run. > > Firmware issues in the original Resolution-T limit those to a 3 second > observation rate. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
Well, with a little prodding and help from Magnus, I now have the Trimble devices outputting RINEX files. They have pseudorange, doppler, and signal strength observations. A 5 hour 1Hz run was sent to CSRS-PPP and the lat/lon/alt error ellipses were in the 250/250/700 mm range... that should improve with a longer run. Firmware issues in the original Resolution-T limit those to a 3 second observation rate. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I repeated the two-receiver test, this time comparing 10 hours of 1 Hz measurements from an LEA-4T with NVS-08C measurments. The NVS has higher resolution RAW data measurements. But, again, the differences in the error ellipses were in the 2-4 mm range. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi, If you move in closer, it will be even more apparent. You do benefit from the improved receivers and the reduced errors translates to better timing error, unless the receivers have other issues. Cheers, Magnus On 06/01/2018 07:36 PM, Bob kb8tq wrote: > Hi > > Indeed, if you look at a 30 minute data file from any of these receivers, it > will not be giving you > quite the same performance. > > Bob > >> On Jun 1, 2018, at 1:00 PM, Magnus Danielson >> wrote: >> >> Hi, >> >> Well, when the resolution and stability is sufficient, other aspects >> weigh in, as being quick to have reduce biases in position and time. >> You can resolve much by averaging etc. but that takes time. >> >> Cheers, >> Magnus >> >> On 06/01/2018 02:10 PM, Bob kb8tq wrote: >>> Hi >>> >>> I can’t say that’s a big surprise. The silicon on these gizmos made it past >>> the “overkill” point at least >>> a decade ago. There’s only so much you can do with a noisy signal ….. Yes, >>> there are indeed feature >>> differences, ( like the Furuno pps ). The core of the device seems to have >>> hit a limit a while ago. >>> >>> Bob >>> On May 31, 2018, at 11:15 PM, Mark Sims wrote: I did another test to see if the M8T offered any positioning advantage over the old (and cheap) LEA-4T and LEA-5T devices. I drove the M8T and LEA-4T with the same antenna, collected data for 12 hours, beamed the RINEX files to Canada. The results matched to within 3mm... so, again, the M8T doesn't offer much benefit for getting precise positions. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. >>> >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi Indeed, if you look at a 30 minute data file from any of these receivers, it will not be giving you quite the same performance. Bob > On Jun 1, 2018, at 1:00 PM, Magnus Danielson > wrote: > > Hi, > > Well, when the resolution and stability is sufficient, other aspects > weigh in, as being quick to have reduce biases in position and time. > You can resolve much by averaging etc. but that takes time. > > Cheers, > Magnus > > On 06/01/2018 02:10 PM, Bob kb8tq wrote: >> Hi >> >> I can’t say that’s a big surprise. The silicon on these gizmos made it past >> the “overkill” point at least >> a decade ago. There’s only so much you can do with a noisy signal ….. Yes, >> there are indeed feature >> differences, ( like the Furuno pps ). The core of the device seems to have >> hit a limit a while ago. >> >> Bob >> >>> On May 31, 2018, at 11:15 PM, Mark Sims wrote: >>> >>> I did another test to see if the M8T offered any positioning advantage over >>> the old (and cheap) LEA-4T and LEA-5T devices. I drove the M8T and LEA-4T >>> with the same antenna, collected data for 12 hours, beamed the RINEX >>> files to Canada. >>> >>> The results matched to within 3mm... so, again, the M8T doesn't offer much >>> benefit for getting precise positions. >>> ___ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi, Well, when the resolution and stability is sufficient, other aspects weigh in, as being quick to have reduce biases in position and time. You can resolve much by averaging etc. but that takes time. Cheers, Magnus On 06/01/2018 02:10 PM, Bob kb8tq wrote: > Hi > > I can’t say that’s a big surprise. The silicon on these gizmos made it past > the “overkill” point at least > a decade ago. There’s only so much you can do with a noisy signal ….. Yes, > there are indeed feature > differences, ( like the Furuno pps ). The core of the device seems to have > hit a limit a while ago. > > Bob > >> On May 31, 2018, at 11:15 PM, Mark Sims wrote: >> >> I did another test to see if the M8T offered any positioning advantage over >> the old (and cheap) LEA-4T and LEA-5T devices. I drove the M8T and LEA-4T >> with the same antenna, collected data for 12 hours, beamed the RINEX files >> to Canada. >> >> The results matched to within 3mm... so, again, the M8T doesn't offer much >> benefit for getting precise positions. >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi I can’t say that’s a big surprise. The silicon on these gizmos made it past the “overkill” point at least a decade ago. There’s only so much you can do with a noisy signal ….. Yes, there are indeed feature differences, ( like the Furuno pps ). The core of the device seems to have hit a limit a while ago. Bob > On May 31, 2018, at 11:15 PM, Mark Sims wrote: > > I did another test to see if the M8T offered any positioning advantage over > the old (and cheap) LEA-4T and LEA-5T devices. I drove the M8T and LEA-4T > with the same antenna, collected data for 12 hours, beamed the RINEX files > to Canada. > > The results matched to within 3mm... so, again, the M8T doesn't offer much > benefit for getting precise positions. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I did another test to see if the M8T offered any positioning advantage over the old (and cheap) LEA-4T and LEA-5T devices. I drove the M8T and LEA-4T with the same antenna, collected data for 12 hours, beamed the RINEX files to Canada. The results matched to within 3mm... so, again, the M8T doesn't offer much benefit for getting precise positions. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi
It’s not real clear what the magic L1 / L2 / L5 gizmo does for you right now
today. As far as I can tell,
the free processing services all only do two at a time. You can do L1 / L2 or
L1 /L5. Possibly at some
point in the future that will change.
Even with “only two” a fancy device will get you down to numbers that simply
are not believable. Any
device that thinks it’s getting into 0.000x meter precision needs to back up
and look at some of the
reference points being used.
Getting back to timing, if you guess that 0.3 m is about a nanosecond, the M8T
is off by about a nanosecond
in lat and lon. It’s off by about 2 ns in elevation. The time solution will be
some sort of RMS of this. Unless
the one and only sat you can see passes directly over you, the full 2 ns isn’t
going to come in.
Location will always be one of a list of errors in getting time data. The
bigger question will be how well the
other stuff on the list is controlled / known. Coming up with an RF delay
number that is good to < 1 ns on
any of these gizmos may be a bit tough…..
If frequency rather than time is the goal, the position error will indeed add
to the “swing” over a day. Your
antenna location / sky view will be a big part of the “how much” part of the
question. You might see a
nanosecond of swing on an hour to hour basis …. you probably would see less.
Simply put, it’s in the
3x10^-12 or less range frequency wise. Most GPSDO’s struggle below a few parts
in 10^-11 for a variety
of reasons ….
Bob
> On May 30, 2018, at 3:46 PM, Mark Sims wrote:
>
> Ok, I did the experiment. I took an 8 hour M8T RINEX file with
> GPS,SBAS,GLONASS,GALILEO data in it. I then used to TEQC to extract GPS only
> and GLONASS only data (CSRS-PPP ignores SBAS and GALILEO data). The 95%
> confidence error ellipse estimates ("rapid" orbits) were:
>
> GPS+GLONASS:lat 0.245mlon 0.219malt 0.582m
> GPS ONLY: lat 0.269mlon 0.239malt 0.616m
> GLONASS ONLY: lat 0.610mlon 0.755malt 1.835m
>
> Conclusion... if you are just interested in an accurate antenna position, a
> $25 LEA-5T should do just fine. GLONASS brings very little benefit (call it
> an inch) to the party. 24 hours of observations can reduce those numbers by
> around 50% I used one of those $70 Chinese L1/L2/GLONASS/BEIDOU antennas
> from Ebay. Note that my antenna location/environment is HORRIBLE...
>
> Things might change if you get into expensive L1+L2(or L5) receivers.
> ___
> time-nuts mailing list -- time-nuts@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
___
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and follow the instructions there.
[time-nuts] nuts about position
Ok, I did the experiment. I took an 8 hour M8T RINEX file with
GPS,SBAS,GLONASS,GALILEO data in it. I then used to TEQC to extract GPS only
and GLONASS only data (CSRS-PPP ignores SBAS and GALILEO data). The 95%
confidence error ellipse estimates ("rapid" orbits) were:
GPS+GLONASS:lat 0.245mlon 0.219malt 0.582m
GPS ONLY: lat 0.269mlon 0.239malt 0.616m
GLONASS ONLY: lat 0.610mlon 0.755malt 1.835m
Conclusion... if you are just interested in an accurate antenna position, a
$25 LEA-5T should do just fine. GLONASS brings very little benefit (call it an
inch) to the party. 24 hours of observations can reduce those numbers by
around 50% I used one of those $70 Chinese L1/L2/GLONASS/BEIDOU antennas from
Ebay. Note that my antenna location/environment is HORRIBLE...
Things might change if you get into expensive L1+L2(or L5) receivers.
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[time-nuts] nuts about position
I finally got in the Ublox M8T and have been testing its RAW data measurements (carrier phase / pseudorange / dopper) data by having Lady Heather write a RINEX file and sending it to CSRS-PPP. Collecting GPS, SBAS, GLONAS, and GALILEO data (CSRS-PPP ignores GALILEO and BEIDOU data) for 2 hours and having it processed with the "ultra rapid" orbits gives a position with around 350 mm lat/lon and 800 mm alt uncertainty ellipse diameter. Using 24 hours of data and the "rapid" (24 hour delayed) orbits gives around 125 mm lat/lon and 300 mm alt uncertainty... the 24 hour file was around 100 MB long, .ZIPed to 25 MB. Not enabling GALILEO would have reduced the file sizes around 25%. I need to see if I can find a program that will split out the GPS/SBAS and GLONAS data into separate RINEX files and see how the two systems compare. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
> > > Results from the Z12 in L1/L2 mode were... iffy... then the receiver died. > The teqc tool from UNAVCO can help with diagnosing iffy data. Can you put your RINEX somewhere? With the antenna in an unobstructed area my Z12 routinely gives 1 cm-ish horizonal, few-cm 3D, using OPUS-S or OPUS-RS. Conceivably there's some reference-clock problem with your Z12 that's trashing the phase observables. As another check, let the unit cool to room temp, then power up and see if it tracks. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
I have Lady Heather's RINEX writer working fairly well. Handles GPS and GLONASS (should also do Galileo when the M8T comes in from Germany... was "in stock" but it took them over a week to ship it). I just did a run on the Furuno GT-8736. It only outputs pseudoranges. A 2.5 hour run @ 1Hz had error ellipses around 0.4 meters lat/lon 1 meter altitude.. similar to a Ublox-5T with pseudoranges and carrier phase. The LEA-5T with 17 hours of 1Hz data were .17 /.15 /.4 meters... not too shabby for a $25 receiver. The NVS-08 with 3 hours of 1Hz GPS/GLONASS data was 0.63/0.59/1.5m (without GLONASS data being processed). Once CSRS-PPP had GLONASS orbit data available, they automatically re-ran it and the error ellipses improved to .57/.56/1.4m A 19 hour/1Hz run on a NVS-08 receiver was 0.175 meters lat/lon .455 meters altitude. Results from the Z12 in L1/L2 mode were... iffy... then the receiver died. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On Sat, May 5, 2018 at 12:08 AM, Mark Sims wrote: > You could add doppler to the RINEX file. All the receivers with raw > messages seem to output that. I think the Doppler measurements can be omitted for static positioning. CSRS-PPP results for a submission with/without Doppler are identical. > I am playing with the Furuno GT87 output. It does not output carrier phase > data (only pseudorange / doppler / SNR). CSRS-PPP can still process that. It seems the carrier phase is not used for single frequency submissions. The summary file says Observation processed: CODE For dual frequency, Observation processed: CODE&PHASE and there are carrier phase residuals in the PDF report. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
You could add doppler to the RINEX file. All the receivers with raw messages seem to output that. I am playing with the Furuno GT87 output. It does not output carrier phase data (only pseudorange / doppler / SNR). CSRS-PPP can still process that. On the first run (3 hours of data, after a 20 minute self-survey ) it did reject 81% of the epochs. Sigmas were 3/2/5 meters. The GT87 outputs altitude as MSL, not WGS84. I just submitted a new 14 hour run (with the receiver doing a self-survey... not in position hold mode). - > I submitted 4 days (118-121) of RINEX files from an IGS station to CSRS-PPP, but with only the GPS C1, L1, and S1 observations. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
I submitted 4 days (118-121) of RINEX files from an IGS station to CSRS-PPP, but with only the GPS C1, L1, and S1 observations. This is similar to what cheap receivers would be generating, but with probably lower noise. emr clocks/orbits were used. The east/north/up differences between the PPP solutions and the latest IGS solution (week 1996) in meters are: E N U -0.29 -0.05 0.14 -0.01 0.12 0.03 0.10 0.11 -0.04 -0.04 0.02 0.65 The reported 95% sigma is 0.26m (longitude), 0.24m (latitude), 0.63m (elevation) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
Hi …… and the quoted errors are in the 10’s of cm range. Thus you need a few years, even if you are moving an inch per year. Bob > On May 3, 2018, at 2:19 PM, Hal Murray wrote: > > > kb...@n1k.org said: >> If you have a very good survey grade receiver and take a long enough data >> set, yes you can watch your location drift in some parts of the world. In >> most locations, fixes a few years apart would be a better bet. > > I'm in Silicon Valley. The San Andreas fault is a few miles from here. A > map of the bay area will show a dozen major faults. A neighborhood map may > have several smaller lines. > https://earthquake.usgs.gov/earthquakes/events/1906calif/virtualtour/bayarea > .php > > The USGS has good GPS receivers sprinkled around the area. You can see > occasional > antenna domes on a post alongside the highway. > http://www.quake.geo.berkeley.edu/usgs-gps/ > (Time sink warning.) > > The fault moves about as fast as your fingernails grow, an inch per year. > That's one side relative to the other. I don't know how fast the pair is > moving. > > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
kb...@n1k.org said: > If you have a very good survey grade receiver and take a long enough data > set, yes you can watch your location drift in some parts of the world. In > most locations, fixes a few years apart would be a better bet. I'm in Silicon Valley. The San Andreas fault is a few miles from here. A map of the bay area will show a dozen major faults. A neighborhood map may have several smaller lines. https://earthquake.usgs.gov/earthquakes/events/1906calif/virtualtour/bayarea .php The USGS has good GPS receivers sprinkled around the area. You can see occasional antenna domes on a post alongside the highway. http://www.quake.geo.berkeley.edu/usgs-gps/ (Time sink warning.) The fault moves about as fast as your fingernails grow, an inch per year. That's one side relative to the other. I don't know how fast the pair is moving. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On 5/3/2018 9:26 AM, Mark Sims wrote: Those results were with the "ultra rapid" orbits. It will be interesting to see what they look like when the final precise orbits are available in a couple of weeks. I also need to see how those values compare to Lady Heather's precision survey results. FWIW, a dual-frequency PPP run I did late last year has the following uncertainties, when processed with the various IGS precision ephemerides, via AUSPOS: longitude latitude altitude IGS UltraRapid 0.004m 0.003m 0.013m IGS Rapid 0.004m 0.003m 0.012m IGS Final 0.004m 0.003m 0.012m The computed ECEF coordinates change by 0.003m(X) and 0.001m(Z) between UltraRapid and Final. ...so really not much of a difference between UltraRapid and Final, at least for a dual-frequency survey at my location. *digs through old stuff* Okay, found a single-frequency survey from mid-last-year, processed by CSRS: longitude latitude altitude NRCan Rapid 0.103m 0.121m 0.253m IGS Final 0.103m 0.121m 0.252m ...not much difference there, either. Both of these were with a roof-mounted antenna and a good skyview, running 24 hours. The first was one measurement every 15 seconds, the latter one measurement per second. (I think for these purposes, one measurement every 15 seconds is more than sufficient and makes the files process *so* much faster). -j ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
In my experience, there is little difference between the Final and Rapid, which will be out just about now (for yesterdays observations) Ole On Thu, May 3, 2018 at 6:26 PM Mark Sims wrote: > To give an idea about the possible improvement in antenna location > available by post-processing the data, I first did a 2 hour self-survey > and that put the receiver into position hold mode. Then I collected RINEX > data for 16 hours. The post-processed lat/lon/alt values differed around > 1/1/3 meters better than the self-survey values (with estimated error > ellipses of 0.17/0.15/0.4 meters). Those results were with the "ultra > rapid" orbits. It will be interesting to see what they look like when the > final precise orbits are available in a couple of weeks. > > I also need to see how those values compare to Lady Heather's precision > survey results. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
To give an idea about the possible improvement in antenna location available by post-processing the data, I first did a 2 hour self-survey and that put the receiver into position hold mode. Then I collected RINEX data for 16 hours. The post-processed lat/lon/alt values differed around 1/1/3 meters better than the self-survey values (with estimated error ellipses of 0.17/0.15/0.4 meters). Those results were with the "ultra rapid" orbits. It will be interesting to see what they look like when the final precise orbits are available in a couple of weeks. I also need to see how those values compare to Lady Heather's precision survey results. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On 5/3/18 8:28 AM, Bob kb8tq wrote: Hi If you have a very good survey grade receiver and take a long enough data set, yes you can watch your location drift in some parts of the world. In most locations, fixes a few years apart would be a better bet. Indeed this does get a bit far from the world of timing …… The distances involved are nasty small. Even for the location of your telescope when doing astronomical timing observations, they are unlikely to matter on a yearly basis. At some point the error is “to small to matter” …. Bob Hit send too quick.. But more realistically, this is kind of a time-nutty sort of goal - to be able to make measurements to a precision where you can match your measurements to a nearby geodetic station with "official" measurements. All the usual time measurement with GPS issues come into it - multipath, the diurnal variations, solid earth tides. It's what everyone says - getting to meters or 10s of ns - easy - getting to tenths of ns or cm, significantly harder. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On 5/3/18 8:28 AM, Bob kb8tq wrote: Hi If you have a very good survey grade receiver and take a long enough data set, yes you can watch your location drift in some parts of the world. In most locations, fixes a few years apart would be a better bet. Indeed this does get a bit far from the world of timing …… The distances involved are nasty small. Even for the location of your telescope when doing astronomical timing observations, they are unlikely to matter on a yearly basis. At some point the error is “to small to matter” …. Bob Unless you live on a plate boundary and have to keep repairing your fences and foundations ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On 5/3/18 8:09 AM, Bob kb8tq wrote: Hi The sites are aimed at improving position information. To the degree that having an accurate location for your antenna improves timing, simply doing that is a step forward for your GPSDO. Most sites also will give you information that shows the timing solution at a given point in time. To the degree that you can connect that to prior data it could be useful. There are more than a few steps involved in getting this to work. The JPL processing chain gives not only more accurate positions vs time, but also estimates of clock error vs time, if that's in the data stream being processed. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
Hi If you have a very good survey grade receiver and take a long enough data set, yes you can watch your location drift in some parts of the world. In most locations, fixes a few years apart would be a better bet. Indeed this does get a bit far from the world of timing …… The distances involved are nasty small. Even for the location of your telescope when doing astronomical timing observations, they are unlikely to matter on a yearly basis. At some point the error is “to small to matter” …. Bob > On May 3, 2018, at 11:12 AM, Artek Manuals wrote: > > To further Chris' question if I took data say on the same day every year can > I measure which way my tectonic plate is moving and how far? > > -DC > manu...@artekmanuals.com > > On 5/3/2018 10:17 AM, Chris Caudle wrote: >> On Wed, May 2, 2018 11:36 pm, Mark Sims wrote: >>> have Heather do all the receiver configuring, data >>> capture, and RINEX making... >> I have been following along with the update messages, and this seems like >> really cool improvements to the underlying infrastructure pieces that a >> lot of us use (Lady Heather, support for more GPS modules, etc.), but I >> am having trouble putting all the pieces together. >> >> Having submitted the files to some post-processing server, do you only get >> back information showing your position to some small number of >> centimeters, or does it send back a stream of values showing the >> corrections to the full position + time equations at each reading? >> Can you use this data to go back to, for example, a stream of timestamps >> and add a correction factor to the timestamps to get improved time >> accuracy on historical data? >> > > -- > Dave > manu...@artekmanuals.com > www.ArtekManuals.com > > > --- > This email has been checked for viruses by Avast antivirus software. > https://www.avast.com/antivirus > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
To further Chris' question if I took data say on the same day every year can I measure which way my tectonic plate is moving and how far? -DC manu...@artekmanuals.com On 5/3/2018 10:17 AM, Chris Caudle wrote: On Wed, May 2, 2018 11:36 pm, Mark Sims wrote: have Heather do all the receiver configuring, data capture, and RINEX making... I have been following along with the update messages, and this seems like really cool improvements to the underlying infrastructure pieces that a lot of us use (Lady Heather, support for more GPS modules, etc.), but I am having trouble putting all the pieces together. Having submitted the files to some post-processing server, do you only get back information showing your position to some small number of centimeters, or does it send back a stream of values showing the corrections to the full position + time equations at each reading? Can you use this data to go back to, for example, a stream of timestamps and add a correction factor to the timestamps to get improved time accuracy on historical data? -- Dave manu...@artekmanuals.com www.ArtekManuals.com --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
Hi The sites are aimed at improving position information. To the degree that having an accurate location for your antenna improves timing, simply doing that is a step forward for your GPSDO. Most sites also will give you information that shows the timing solution at a given point in time. To the degree that you can connect that to prior data it could be useful. There are more than a few steps involved in getting this to work. Bob > On May 3, 2018, at 10:17 AM, Chris Caudle wrote: > > On Wed, May 2, 2018 11:36 pm, Mark Sims wrote: >> have Heather do all the receiver configuring, data >> capture, and RINEX making... > > I have been following along with the update messages, and this seems like > really cool improvements to the underlying infrastructure pieces that a > lot of us use (Lady Heather, support for more GPS modules, etc.), but I > am having trouble putting all the pieces together. > > Having submitted the files to some post-processing server, do you only get > back information showing your position to some small number of > centimeters, or does it send back a stream of values showing the > corrections to the full position + time equations at each reading? > Can you use this data to go back to, for example, a stream of timestamps > and add a correction factor to the timestamps to get improved time > accuracy on historical data? > > -- > Chris Caudle > > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On Wed, May 2, 2018 11:36 pm, Mark Sims wrote: > have Heather do all the receiver configuring, data > capture, and RINEX making... I have been following along with the update messages, and this seems like really cool improvements to the underlying infrastructure pieces that a lot of us use (Lady Heather, support for more GPS modules, etc.), but I am having trouble putting all the pieces together. Having submitted the files to some post-processing server, do you only get back information showing your position to some small number of centimeters, or does it send back a stream of values showing the corrections to the full position + time equations at each reading? Can you use this data to go back to, for example, a stream of timestamps and add a correction factor to the timestamps to get improved time accuracy on historical data? -- Chris Caudle ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
Hi Thank goodness it now is almost all self contained. Typing three or for lines of a script is *so* last century :) Sounds very cool !! LH continues to do amazing things. She is an impressive lady. Do you ever have time to sleep? My guess is that some sort of write up for doing the submittal to each of the “likely victim” agencies will be needed. Then of course there is the data reduction and plotting on the returned file …… hmmm …… :) Bob > On May 3, 2018, at 3:56 AM, Mark Sims wrote: > > Woohoo! Success!I sent a RINEX 2.10 formatted .obs file generated by > Heather from a Ublox 5 to Canada for post-processing. The results matched > those from RTKLIB processing to within 1mm. Oh, and on noth cases the > post-processing used the "emu" orbit info. > > I haven't heard back from Australia, but I think the file that I sent down > under has some duplicate data block errors. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
Woohoo! Success!I sent a RINEX 2.10 formatted .obs file generated by Heather from a Ublox 5 to Canada for post-processing. The results matched those from RTKLIB processing to within 1mm. Oh, and on noth cases the post-processing used the "emu" orbit info. I haven't heard back from Australia, but I think the file that I sent down under has some duplicate data block errors. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
The goal is to make it as simple as possible and have Heather do all the receiver configuring, data capture, and RINEX making... with none of that tedious mucking about in RTKLIB Currently all I have to do is fire up Heather and tell it to write a log file with the .obs extension. -- > RTKLIB's RTKCONV can convert between RINEX versions. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On Thu, May 3, 2018 at 9:40 AM, Mark Sims wrote: > G... Canada lives in the dark ages and does not accept RINEX version > 3... I'm now trying Australia... > > Version 3 is cleaner and easier to write than Version 2... > RTKLIB's RTKCONV can convert between RINEX versions. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
I tried submitting Version 3 files to several services... none support Version 3!Heather now creates the uglier/less readable Version 2.10 RINEX, ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
G... Canada lives in the dark ages and does not accept RINEX version 3... I'm now trying Australia... Version 3 is cleaner and easier to write than Version 2... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
For the orbits is says "Precise", so maybe not even the hourly ones. I could not find any mention of emu, emr, or igs. Heather can now spit out Rinex 3.02 files (at least for GPS/SBAS sats).I am currently feeding Heather the .raw capture file I sent to Canada and outputting a RINEX .OBS file. I'll send that off to them and see if there is any difference in the results from the one from RTKCONV. The RTKCONV processed values for pseudo ranges and carrier phase values seems to have been tweaked from what the receiver sent... they differ by a fractional amount. - > Was the solution using the NRCan hourly's or the IGS Rapid products ? (It should say in the email response or the .sum file: the 'Satellite orbits/clocks' lines seem to have 'emu', 'emr' or 'igs' for the NRCan hourly/UltraRapid, Rapid and Final solutions respectively). ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (cheap receiver)
On Wed, May 2, 2018 at 2:54 PM, Mark Sims wrote: > Well, I processed the Lady Heather .raw capture file from the $24 LEA-5T > through RTKCONV and submitted it to CSRS-PPP and it worked. Using the less > precise instant orbits it says the 95% sigma errors are: lat: 0.169m > lon:0.148m alt: 0.399m > > My antenna is that Chinese L1/L2/Glonass/etc antenna from ebay. I'll > re-submit the data next week and see how it changes. Was the solution using the NRCan hourly's or the IGS Rapid products ? (It should say in the email response or the .sum file: the 'Satellite orbits/clocks' lines seem to have 'emu', 'emr' or 'igs' for the NRCan hourly/UltraRapid, Rapid and Final solutions respectively). Submittals less than a day after the observations in the RINEX file seem to result in the use of the Hourly/UltraRapids solutions. Cheers, Tim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
Well, I processed the Lady Heather .raw capture file from the $24 LEA-5T through RTKCONV and submitted it to CSRS-PPP and it worked. Using the less precise instant orbits it says the 95% sigma errors are: lat: 0.169m lon:0.148m alt: 0.399m My antenna is that Chinese L1/L2/Glonass/etc antenna from ebay. I'll re-submit the data next week and see how it changes. Also, I now sort-of have Heather outputting a RINEX 3.02 format .OBS file. Oh, and Bob... Heather can run an external program at a given time or after a specified interval, so could be set up to automatically submit the file... you lazy bastard ;-) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position (cheap receiver)
There are some sellers on Ebay LEA-5T receivers on Ebay for cheap. They are pin and layout compatible with the Trimble Resolution-T devices. I bought a couple from this guy ($24 each) and they do output the RAW and SFRB messages. He also has LEA-4T and Trimble boards. There are also other sellers that are more expensive... search for LEA-5T https://www.ebay.com/itm/Ublox-LEA-5T-GPS-MODULE-BOARD/253584793155?hash=item3b0ad4de43:g:6CEAAOSwEZdZ7Z-7 I have not tried to post-process the data yet. I currently have Heather doing a raw data capture... ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On Tue, May 1, 2018 at 2:14 PM, Hal Murray wrote: > > kb...@n1k.org said: >> One important qualifier to re-state. L1 post processing is very dependent on >> the distance to an “open” source of correction data. The spacing of those >> sites over the US is highly variable. If you get outside the US it is very >> much a “that depends” sort of thing. Some countries apparently don’t have >> the same sort of open site network > > Is there a map of the available locations? > Hi Hal, There are maps for IGS [1], CORS [2], and EUREF [3] stations (and probably others I'm not familiar with). For those three, RINEX obs data can be downloaded if you want to do post processing with RTKLIB. Centimeter-level static relative positioning is possible with single frequency receivers and a reference station that is near (~10 km, maybe more depending on the ionosphere). [1] http://www.igs.org/network [2] https://www.ngs.noaa.gov/CORS_Map/ [3] http://www.epncb.oma.be/_networkdata/stationmaps.php ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I added some debug log info that shows how many bytes the receiver sent between time messages. The LEA-6T sends around 500-600 bytes every second. That fits easily into 9600 baud. The M8N tracking all sats and with all the raw messages enabled spews around 4000 bytes. That would require 57,600 baud. It looks like M8N's with standard firmware are not suitable for precise positioning. They do not output the required RAW data messages: https://rtklibexplorer.wordpress.com/2017/06/07/newest-u-blox-m8n-receivers-not-usable-with-rtklib/ Various GPS receivers handle transmit buffer overflows in different ways... including various combinations of dropping messages, garbling data, or crashing. Most receivers seem to have transmit/receiver buffers in the 1000 byte range... some are smaller, some are larger. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi The “drops stuff” problem is exactly what I saw trying to run at lower baud rates. The port is *not* full of data, there’s plenty of time to get it all out at a lower baud rate. For some reason (buffers maybe) these modules start dropping data *way* earlier than you would think they should. Bob > On Apr 30, 2018, at 10:48 PM, Mark Sims wrote: > > I once spent way too much time trying to get Heather to spit out a RINEX file > from a Thunderbolt. I could never get any of the post-processors to accept > it. The Thunderbolt's raw data needs to somehow be tweaked to be compatible > and I didn't really know what I was doing. > > A LEA-6T seems to be able to cope with the data stream at it's default 9600 > baud. I just tried a NEO-8N and it drops packets, etc. Even weirder, it > does not output any of the requested packets that might be flooding the port, > but still drops packets. > > > --- > >> You mean that LH does not translate the data to the correct format *and* >> submit it for post processing ? > > There *is* a lot of data when you turn all this stuff on. If you can get > above 115K baud, it’s well worth it. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
kb...@n1k.org said: > One important qualifier to re-state. L1 post processing is very dependent on > the distance to an âopenâ source of correction data. The spacing of those > sites over the US is highly variable. If you get outside the US it is very > much a âthat dependsâ sort of thing. Some countries apparently donât > have > the same sort of open site network Is there a map of the available locations? Do the RINEX processors tell you which ones they used? With maybe a note if the one they would like to use is not working properly. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
Heather now requests the RAW and RAWX messages... those output carrier phase, doppler, and pseudo ranges.The M8N does not support either, but the M8T supports RAWX. Heather now requests the SFRB and SFRBX messages... those output the satellite navigation messages. All the M8's output SFRBX. I cranked up the M8N baud rate to 115200 and the receiver can handle all the various raw messages But the bugaboo is requesting the TRK-MEAS and TRK-SFRBX messages. The messages are not officially supported, Ublox forbids talking about them on their forums... they might even dispatch Ninja assassins if you talk about them. If you request those messages on the M8N very bad things seem to happen... you start receiving messages 0x27-0x00 with a length of either 68 bytes or around 1300-1400 bytes. Whatever 0x27-0x00 is, nobody's talking... The 0x27 message group is for security features like chip serial numbers. I have an M8T on the way from Germany... -- > I think heather is parsing the UBX_RAW_RATE messages for the raw GPS meansurements. The LEA-6T allows UBX_RAW_RATE, but the NEO-M8N does not. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Yo Mark! On Tue, 1 May 2018 02:48:17 + Mark Sims wrote: > A LEA-6T seems to be able to cope with the data stream at it's > default 9600 baud. I just tried a NEO-8N and it drops packets, I think heather is parsing the UBX_RAW_RATE messages for the raw GPS meansurements. The LEA-6T allows UBX_RAW_RATE, but the NEO-M8N does not. RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin pgpX8JFrYGSwt.pgp Description: OpenPGP digital signature ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I once spent way too much time trying to get Heather to spit out a RINEX file from a Thunderbolt. I could never get any of the post-processors to accept it. The Thunderbolt's raw data needs to somehow be tweaked to be compatible and I didn't really know what I was doing. A LEA-6T seems to be able to cope with the data stream at it's default 9600 baud. I just tried a NEO-8N and it drops packets, etc. Even weirder, it does not output any of the requested packets that might be flooding the port, but still drops packets. --- > You mean that LH does not translate the data to the correct format *and* > submit it for post processing ? There *is* a lot of data when you turn all this stuff on. If you can get above 115K baud, it’s well worth it. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi You mean that LH does not translate the data to the correct format *and* submit it for post processing ? There *is* a lot of data when you turn all this stuff on. If you can get above 115K baud, it’s well worth it. = One important qualifier to re-state. L1 post processing is very dependent on the distance to an “open” source of correction data. The spacing of those sites over the US is highly variable. If you get outside the US it is very much a “that depends” sort of thing. Some countries apparently don’t have the same sort of open site network that we have in the US. Bob > On Apr 30, 2018, at 4:36 PM, Mark Sims wrote: > > Coincidentally, yesterday I tweaked up Lady Heather's Ublox code to enable > all of the necessary raw data messages. Heather also enables the raw > messages from Trimble TSIP speaking receivers, the NVS CSM24 receiver, and > the Furuno GT87 receiver (if baud rate is >=115200). > > Heather can write a raw data capture file (/dr=filename on the command line > or WY from the keyboard). You should be able to convert those raw capture > files to RINEX and then post-process those. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
Coincidentally, yesterday I tweaked up Lady Heather's Ublox code to enable all of the necessary raw data messages. Heather also enables the raw messages from Trimble TSIP speaking receivers, the NVS CSM24 receiver, and the Furuno GT87 receiver (if baud rate is >=115200). Heather can write a raw data capture file (/dr=filename on the command line or WY from the keyboard). You should be able to convert those raw capture files to RINEX and then post-process those. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi If you are looking at doing a self survey on a timing module, there is a lot of information in the archives. It turns out that (like it or not) there is very likely to be a ~24 hour periodicity in your self survey data. Therefor something like a two, three, or four day survey will enhance your position estimate. Again - for all get gory details dig into the archives. Since the timing is done against the module’s “best estimate” of it’s position, there isn’t a lot of benefit in having a surveyed correct position instead. More or less, the same errors that goofed the position also goof the timing in the same direction. Again, info in the archives. Bob > On Apr 30, 2018, at 2:41 PM, Achim Gratz wrote: > > Tim Lister writes: >> It has taken me quite a bit longer that I had hoped but I have finally >> published a writeup and howto of collecting raw ublox data, converting >> it to RINEX and how to do (or get the NRC experts to do) the >> post-processing. It's at a new website I have setup: >> https://adventuresinprecision.space/howtos/precise-gps-positions/ >> Please let me know any comments or suggestions you have to improve it >> or make it more comprehensible and comprehensive. > > Thanks for taking the time to write that up. Out of curiosity, how far > away from the RINEX coordinates is an RMS or median of the original > coordinates as recorded by the GPS and how does the convergence curve > look like? I'm trying to gauge how long I need to run my timing module > in survey mode… > > > Regards, > Achim. > -- > +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ > > Wavetables for the Waldorf Blofeld: > http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Tim Lister writes: > It has taken me quite a bit longer that I had hoped but I have finally > published a writeup and howto of collecting raw ublox data, converting > it to RINEX and how to do (or get the NRC experts to do) the > post-processing. It's at a new website I have setup: > https://adventuresinprecision.space/howtos/precise-gps-positions/ > Please let me know any comments or suggestions you have to improve it > or make it more comprehensible and comprehensive. Thanks for taking the time to write that up. Out of curiosity, how far away from the RINEX coordinates is an RMS or median of the original coordinates as recorded by the GPS and how does the convergence curve look like? I'm trying to gauge how long I need to run my timing module in survey mode… Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ Wavetables for the Waldorf Blofeld: http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On Wed, Apr 25, 2018 at 8:38 AM, Tim Lister wrote: > On Wed, Apr 25, 2018 at 7:56 AM, Tom Van Baak wrote: >> List -- I had a recent query by a researcher who would like to pinpoint the >> location of his telescope(s) within 0.3 meters. Also (he must be a true >> scientist) he wants to do this on-the-cheap. He may have timing requirements >> as well, but that's another posting. >> >> So I toss the GPS question to the group. Surely some of you have crossed the >> line from precise time to precise location? >> >> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D >> position? >> >> When we run our GPSDO in survey mode how accurate a position do we get after >> an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have >> any of you compared that self-reported, self-survey result against an >> independently measured professional result or known benchmark? >> >> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot >> accuracy given enough time? >> >> If not, what improvement would -T models and RINEX-based web-service >> post-processing provide? >> >> It that's still not close enough to 0.3 m, is one then forced to use more >> expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to >> achieve this level of precision? If so, how cheaply can one do this? Or is >> the learning curve more expensive than just hiring an survey specialist to >> make a one-time cm-level measurement for you? >> >> Something tells me 1 foot accuracy in position is possible and actually >> easier than 1 ns accuracy in time. I'm hoping some of you can help recommend >> solution(s) to the researcher's question or shed light on this interesting >> challenge. > > Hi Tom, list, as another researcher who is also interested in > telescope positions (!) I have done this for personal use at home with > a ublox 6T and 53532A antenna to see what I got. I was logging in the > UBX binary format with the raw (carrier phase) measurements turned on > and then converting it to RINEX and using the NRC's CSRS-PPP online > service which is one of the few that will take single frequency L1 > only data. The results based on approx. 41.5 hours of data and which > were post-processed 21 days later (so that they used the IGS Final > products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of > 0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal > height respectively. I was quite impressed with the results without > use of the L2 frequency to correct for the ionosphere etc. It has taken me quite a bit longer that I had hoped but I have finally published a writeup and howto of collecting raw ublox data, converting it to RINEX and how to do (or get the NRC experts to do) the post-processing. It's at a new website I have setup: https://adventuresinprecision.space/howtos/precise-gps-positions/ Please let me know any comments or suggestions you have to improve it or make it more comprehensible and comprehensive. I have also been doing some experiments with RTK solutions with local precise base stations and receiving NTRIP correction messages over RTCM. This is looking very promising but I need to do some more experiments (and as detailed in the howto, wait for some more precise products to be available to compare it with...) Cheers, Tim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position (Michael Wouters)
Here is a pretty good paper (as far as I can tell) from 2017 looking at ways to improve single frequency results: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5492347/ > 28. apr. 2018 kl. 06:20 skrev Jerome Blaha : > > Real-time GPS <0.3m accuracy is quite possible with RTKLIB and < $35 of new > equipment, some patience, a laptop/android phone, and a real-time RTCM3 > correction station stream (free) or with post-processing using ground > stations and actual satellite path (Ephemeris). > > Disclaimer: I am neither a surveyor nor claimed GPS expert, but I play one on > TV with my day job, so consult a surveyor if you are having to survey in > WGS84 datum and convert to NAD or some other reference system, especially if > testing against old surveyed reference points. For instance here in the SF > Bay Area, the land is moving North 28.31mm/yr and West 21.87mm/yr with > respect to the WGS-84 (GPS Position) datum, which uses satellites orbits and > the earth center as their reference. If you were to survey your Telescope > position in WGS-84 in the Bay Area, wait 15 years and survey again, the > telescope will appear to have moved Northwest by 53.7cm and will have moved > down by 1.1cm (Assumptions taken from SLAC de-trended data here: > https://www.unavco.org/data/gps-gnss/derived-products/position-timeseries/SLAC_timeseries_cleaned_detrended.png) > > This is why most surveying is performed not in WGS-84 but in a datum that > remains fixed to a tectonic plate as it moves, such as NAD83. The 83 refers > to the date or year (epoch) when the land position or survey marker was at > that location, because even surveyed positions can move over time within that > same tectonic reference frame such as along fault-lines, etc. > > Getting back, RTKLIB is a brilliant piece of open-source software to allow > sub-meter (<5cm) phase-based positioning and my hat goes off to Tomoji Takasu > from Japan who wrote this and keeps updating it. Very few GPS receivers can > measure phase shift, so this is where a specialized L1 + L2 survey receiver > is needed or you find a cheap L1 GPS chip capable of raw phase and code, such > as the u-blox M6T or M8T. > > > RECEIVER: > With regards to a GPS + Glonass raw receiver, the cheapest ublox M8T > legitimate supplier seems to be over at csgshop.com in Northern Europe. He > has the real M8T GPS for $75 and I secretly believe he might also be one of > the test engineers for u-blox. I say real, because there are knock-offs on > ebay. > > Why did I mention $35? Well, you can find an M6T gps-only with raw ublox > output on Amazon and elsewhere called LEA-6T that should get the job done if > you add a metal ground plane. This little thing works surprisingly well when > tested for repeatable RTK fixes within 5cm and you can even do a real-time > RTK fixes with only an Android phone and the older RTK lib App on GooglePlay. > (M8T not supported) Don't feel you have to use a newer M8T with GPS + > Glonass, as usually a GPS-only solution will be superior to a GPS + Gloanss, > because Glonass seems to have a little more noise to it. (Discussion for > another time) > > > USGS SURVEY MARKERS > While we're at it, let's mention that there are survey points all over the > United States where you can test the accuracy of your newly working RTK GPS > system. These are markers placed by the USGS and are typically reported in > NAD or other American datum format. These must be converted to WGS-84 datum > for you to compare with GPS positions and there are tools out there if you do > a Google search for converting datums to WGS-84, just pay attention to what > year(epoch) you are converting to and it gets tricky to wrap your head around > conversion between different Ellipsoids and Geoids (ground height). > https://www.ngs.noaa.gov/NGSDataExplorer/ > > > RTKLIB: > RTKLIB has multiple tools to allow streaming, real-time, logging, > post-processing, and graphing RTK GPS fixes. Typically raw GPS (code & phase > measurements) are converted to RINEX data format before post-processing. > RINEX is a standard and allows for raw GPS code and phase measurements > between different GPS manufactures into one format for processing in > third-party software. > > RTKLIB works in Windows and is a little tough to get started with; thankfully > there is another very nice guy, Tim Everett, who has written many articles at > rtkexplorer.com on accuracy of cheap RTK gps chips interfaced with RTKLIB as > well as tutorials on getting started with pretty pictures. As a side note, > you may be tempted to try a newer ublox M8N; however many M8N chips are > firmware disabled to not give raw phase anymore without firmware hacking. > (The M8T still works with RTKLIB 2.4.3) > > > SATELLITE PATH (EPHEMERIS) > When typical GPS receivers are running in real-time, they download an > approximate ephemeris of where the satellite path flies within a meter
Re: [time-nuts] nuts about position (Michael Wouters)
Real-time GPS <0.3m accuracy is quite possible with RTKLIB and < $35 of new equipment, some patience, a laptop/android phone, and a real-time RTCM3 correction station stream (free) or with post-processing using ground stations and actual satellite path (Ephemeris). Disclaimer: I am neither a surveyor nor claimed GPS expert, but I play one on TV with my day job, so consult a surveyor if you are having to survey in WGS84 datum and convert to NAD or some other reference system, especially if testing against old surveyed reference points. For instance here in the SF Bay Area, the land is moving North 28.31mm/yr and West 21.87mm/yr with respect to the WGS-84 (GPS Position) datum, which uses satellites orbits and the earth center as their reference. If you were to survey your Telescope position in WGS-84 in the Bay Area, wait 15 years and survey again, the telescope will appear to have moved Northwest by 53.7cm and will have moved down by 1.1cm (Assumptions taken from SLAC de-trended data here: https://www.unavco.org/data/gps-gnss/derived-products/position-timeseries/SLAC_timeseries_cleaned_detrended.png) This is why most surveying is performed not in WGS-84 but in a datum that remains fixed to a tectonic plate as it moves, such as NAD83. The 83 refers to the date or year (epoch) when the land position or survey marker was at that location, because even surveyed positions can move over time within that same tectonic reference frame such as along fault-lines, etc. Getting back, RTKLIB is a brilliant piece of open-source software to allow sub-meter (<5cm) phase-based positioning and my hat goes off to Tomoji Takasu from Japan who wrote this and keeps updating it. Very few GPS receivers can measure phase shift, so this is where a specialized L1 + L2 survey receiver is needed or you find a cheap L1 GPS chip capable of raw phase and code, such as the u-blox M6T or M8T. RECEIVER: With regards to a GPS + Glonass raw receiver, the cheapest ublox M8T legitimate supplier seems to be over at csgshop.com in Northern Europe. He has the real M8T GPS for $75 and I secretly believe he might also be one of the test engineers for u-blox. I say real, because there are knock-offs on ebay. Why did I mention $35? Well, you can find an M6T gps-only with raw ublox output on Amazon and elsewhere called LEA-6T that should get the job done if you add a metal ground plane. This little thing works surprisingly well when tested for repeatable RTK fixes within 5cm and you can even do a real-time RTK fixes with only an Android phone and the older RTK lib App on GooglePlay. (M8T not supported) Don't feel you have to use a newer M8T with GPS + Glonass, as usually a GPS-only solution will be superior to a GPS + Gloanss, because Glonass seems to have a little more noise to it. (Discussion for another time) USGS SURVEY MARKERS While we're at it, let's mention that there are survey points all over the United States where you can test the accuracy of your newly working RTK GPS system. These are markers placed by the USGS and are typically reported in NAD or other American datum format. These must be converted to WGS-84 datum for you to compare with GPS positions and there are tools out there if you do a Google search for converting datums to WGS-84, just pay attention to what year(epoch) you are converting to and it gets tricky to wrap your head around conversion between different Ellipsoids and Geoids (ground height). https://www.ngs.noaa.gov/NGSDataExplorer/ RTKLIB: RTKLIB has multiple tools to allow streaming, real-time, logging, post-processing, and graphing RTK GPS fixes. Typically raw GPS (code & phase measurements) are converted to RINEX data format before post-processing. RINEX is a standard and allows for raw GPS code and phase measurements between different GPS manufactures into one format for processing in third-party software. RTKLIB works in Windows and is a little tough to get started with; thankfully there is another very nice guy, Tim Everett, who has written many articles at rtkexplorer.com on accuracy of cheap RTK gps chips interfaced with RTKLIB as well as tutorials on getting started with pretty pictures. As a side note, you may be tempted to try a newer ublox M8N; however many M8N chips are firmware disabled to not give raw phase anymore without firmware hacking. (The M8T still works with RTKLIB 2.4.3) SATELLITE PATH (EPHEMERIS) When typical GPS receivers are running in real-time, they download an approximate ephemeris of where the satellite path flies within a meter or two. The final ephemeris is the best true path that the GPS satellite actually flew, down to 10cm, however these files are not available until more than a week after you collect your raw survey by going to a government website such as (https://www.ngs.noaa.gov/orbits/orbit_data.shtml) These post-processed orbital paths are computed from hundred of surveyed ground stations
Re: [time-nuts] nuts about position
The US-based services work fine with non-local data. I've used them with Australian locations. The IGS network is global so nearby stations in the IGS network are used for the solution. There are non-US services too, like AusPos. The topic of better antenna coordinates seems to come up now and again. It might be a good cooperative timenuts project to put together a travelling receiver system that could be used to survey antenna positions. With a bit more effort, it could also be used to calibrate delays, where receiver data is being post-processed for time-transfer. Cheers Michael On Fri, 27 Apr 2018 at 8:02 am, Bob kb8tq wrote: > Hi > > If you shop for a while on eBay, you can find older L1 / L2 survey > receivers for < $300 and > an antenna that will work for them for < $100. Yes it will take a bit of > heavy duty shopping and > some level of “wait and see”. How well they work and how much of a pain > is associated with > this process ….. who knows. > > Once you have a radio you can get data out of, submitting the files to any > of the free services > in the US is pretty easy. If you are outside the US, you may still be fine > or you may have a tough > time with the data reduction. > > Bob > > > On Apr 26, 2018, at 1:04 PM, Scott McGrath wrote: > > > > Swiftnav has a centimeter accurate multi band receiver RTK-585. Its > about 600 bucks minus antenna. > > > > You would need a choke ring antenna to get centimeter accuracy i think > but receiver with a quality timing antenna will provide necessary accuracy > > > > On Apr 25, 2018, at 8:06 AM, George Watson wrote: > > > > Create your own DGPS? > > > > Trimble is good at this. > > > > George K. Watson > > K0IW > > > >> On Apr 25, 2018, at 10:56 AM, Tom Van Baak wrote: > >> > >> List -- I had a recent query by a researcher who would like to pinpoint > the location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing > requirements as well, but that's another posting. > >> > >> So I toss the GPS question to the group. Surely some of you have > crossed the line from precise time to precise location? > >> > >> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > >> > >> When we run our GPSDO in survey mode how accurate a position do we get > after an hour, or even 24 or 48 hours? And here I mean accurate, not > stable. Have any of you compared that self-reported, self-survey result > against an independently measured professional result or known benchmark? > >> > >> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 > foot accuracy given enough time? > >> > >> If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > >> > >> It that's still not close enough to 0.3 m, is one then forced to use > more expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, > Galileo) to achieve this level of precision? If so, how cheaply can one do > this? Or is the learning curve more expensive than just hiring an survey > specialist to make a one-time cm-level measurement for you? > >> > >> Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help > recommend solution(s) to the researcher's question or shed light on this > interesting challenge. > >> > >> Thanks, > >> /tvb > >> > >> ___ > >> time-nuts mailing list -- time-nuts@febo.com > >> To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > >> and follow the instructions there. > >> > > > > ___ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > ___ > > time-nuts mailing list -- time-nuts@febo.com > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On Thu, Apr 26, 2018 at 12:08 PM, Gary E. Miller wrote: > Scott! > > On Thu, 26 Apr 2018 10:04:54 -0700 > Scott McGrath wrote: > >> Swiftnav has a centimeter accurate multi band receiver RTK-585. Its >> about 600 bucks minus antenna. > > Link? With RTK in the name it prolly needs a base and rover? Or post > processing? It's this one: https://www.swiftnav.com/piksi-multi One thing to bear in mind is it only L2C, the new civilian channel on the lower frequency L2 band. This is not available on approx. 1/2 of the satellites currently. There are several articles evaluating in comparison with e.g. a ublox M8T at https://rtklibexplorer.wordpress.com/tag/swift-piksi-multi/ > > RGDS > GARY Cheers, Tim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi If you shop for a while on eBay, you can find older L1 / L2 survey receivers for < $300 and an antenna that will work for them for < $100. Yes it will take a bit of heavy duty shopping and some level of “wait and see”. How well they work and how much of a pain is associated with this process ….. who knows. Once you have a radio you can get data out of, submitting the files to any of the free services in the US is pretty easy. If you are outside the US, you may still be fine or you may have a tough time with the data reduction. Bob > On Apr 26, 2018, at 1:04 PM, Scott McGrath wrote: > > Swiftnav has a centimeter accurate multi band receiver RTK-585. Its about 600 > bucks minus antenna. > > You would need a choke ring antenna to get centimeter accuracy i think but > receiver with a quality timing antenna will provide necessary accuracy > > On Apr 25, 2018, at 8:06 AM, George Watson wrote: > > Create your own DGPS? > > Trimble is good at this. > > George K. Watson > K0IW > >> On Apr 25, 2018, at 10:56 AM, Tom Van Baak wrote: >> >> List -- I had a recent query by a researcher who would like to pinpoint the >> location of his telescope(s) within 0.3 meters. Also (he must be a true >> scientist) he wants to do this on-the-cheap. He may have timing requirements >> as well, but that's another posting. >> >> So I toss the GPS question to the group. Surely some of you have crossed the >> line from precise time to precise location? >> >> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D >> position? >> >> When we run our GPSDO in survey mode how accurate a position do we get after >> an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have >> any of you compared that self-reported, self-survey result against an >> independently measured professional result or known benchmark? >> >> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot >> accuracy given enough time? >> >> If not, what improvement would -T models and RINEX-based web-service >> post-processing provide? >> >> It that's still not close enough to 0.3 m, is one then forced to use more >> expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to >> achieve this level of precision? If so, how cheaply can one do this? Or is >> the learning curve more expensive than just hiring an survey specialist to >> make a one-time cm-level measurement for you? >> >> Something tells me 1 foot accuracy in position is possible and actually >> easier than 1 ns accuracy in time. I'm hoping some of you can help recommend >> solution(s) to the researcher's question or shed light on this interesting >> challenge. >> >> Thanks, >> /tvb >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Scott! On Thu, 26 Apr 2018 10:04:54 -0700 Scott McGrath wrote: > Swiftnav has a centimeter accurate multi band receiver RTK-585. Its > about 600 bucks minus antenna. Link? With RTK in the name it prolly needs a base and rover? Or post processing? RGDS GARY --- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Swiftnav has a centimeter accurate multi band receiver RTK-585. Its about 600 bucks minus antenna. You would need a choke ring antenna to get centimeter accuracy i think but receiver with a quality timing antenna will provide necessary accuracy On Apr 25, 2018, at 8:06 AM, George Watson wrote: Create your own DGPS? Trimble is good at this. George K. Watson K0IW > On Apr 25, 2018, at 10:56 AM, Tom Van Baak wrote: > > List -- I had a recent query by a researcher who would like to pinpoint the > location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing requirements > as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed the > line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get after > an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have > any of you compared that self-reported, self-survey result against an > independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help recommend > solution(s) to the researcher's question or shed light on this interesting > challenge. > > Thanks, > /tvb > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On Wed, 25 Apr 2018 18:02:53 -0400, time-nuts-requ...@febo.com wrote: > time-nuts Digest, Vol 165, Issue 50 > > Message: 3 > Date: Wed, 25 Apr 2018 10:19:38 -0500 > From: Dana Whitlow > To: Tom Van Baak , Discussion of precise time and > frequency measurement > Subject: Re: [time-nuts] nuts about position > Message-ID: > > Content-Type: text/plain; charset="UTF-8" > > While I was at the Arecibo Observatory it became desirable to get a good > surveyed position > for a new GPS antenna we had installed for the NIST TMAS system. We found > a resource > at the Univ of Puerto Rico who had a Trimble (I think) unit. He set it up > on the site, "turned on > the bubble machine", then left it alone for about two hours. He returned > the estimated > position a few days later, expressing high confidence that it was good > within about 8 inches. > > I'm sure I asked him if this machine used both L1 & L2, but don't recall > his answer. I suspect it was "yes". It will have been using carrier phase only, not the L2 modulation (which is encrypted). Although one can do correlation on the L2 modulation from a given satellite in common view as well. Joe Gwinn ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi On something like a phone, you are likely looking at a combination of what the phone does and a contribution from “the cloud”. Part of that cloud contribution depends a bit on the carrier and how well they are doing their part of things. In one area you might have surveyed towers and a full GPS / Glonass synthesis. If you bought your service from Crazy Bob, there may be no local correction information. Forget about GPS / Glonass in that case (at least in the US). Bob > On Apr 25, 2018, at 10:46 PM, Brooke Clarke wrote: > > Hi J: > > I had a number of survey stakes I placed using a manual transit and tape > measure and hired a local surveyor to tell me where they were and also tell > me where my GPS antenna was located. > > He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total > station on another tripod and ran a cable between the two. After some time > (tens of minutes or ??) he used the theodolite to sight my stakes and the GPS > antenna. I got a report back in a week or so. Total cost a few hundred > dollars. > > I'm in the process of looking at how accurate the GPS is in my new LG G6 > phone. > > -- > Have Fun, > > Brooke Clarke > http://www.PRC68.com > http://www.end2partygovernment.com/2012Issues.html > > Original Message >> I think to really be confident about a position you really need the >> dual-frequency data (or that data from a nearby reference station), >> otherwise you could end up in a situation where you're consistent, but that >> consistency has a bias. IIRC, anyhow -- I'm not sure how the math actually >> works out. >> >> Anyhow, I play around with PPP stuff on occasion, and the last run I did was >> in November using the Novatel OEM628 kit that was briefly available for >> cheap on eBay, and the included 702-GG antenna (which, conveniently, has >> calibrations available). Running a day's worth of data through CSRS-PPP >> produced sigmas (95%) of 0.004m latitude, 0.008m longitude, and 0.024m in >> elevation. I've done some shorter runs since then that appear to fall in >> that same range ... I really need to do a few more full runs and see what >> kind of variance there is. >> >> At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even >> takes solid earth tides into account, though I didn't do that because I was >> never able to figure out which specific type of solid earth tide data I >> needed. I imagine there's still some issues with any given datum being >> somewhat imperfect, as far as altitude is concerned, and I don't really know >> how to correctly deal with that if exact altitude matters. Maybe we should >> all just agree to use XYZ/ECEF coordinates for everything and give up on >> this whole altitude thing altogether... ;) >> >> (As an aside, I've been tempted to get someone to come professionally survey >> my antenna and tell me where it _actually_ is, so I could see how well I >> could actually do with my GPS kit, but I imagine it's pretty expensive -- >> anyone happen to know what getting that kind of thing done actually ends up >> costing?) >> >> -j > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi I just ran a quick test - a Ublox 6T was configured to output the RXM-RAW messages every second and logging for some 14 hours using U-Center. The .ubx-file was converted to RINEX using teqc.exe, and uplaoded to NrCAN PPP. NrCAN PPP will process single frequency observations and correct using ionospheric maps I *believe*. (If I am wrong, ignore this post!) I also continously log observations from a Trimble NetRS dual frequency GPS receiver, hooked up to the same antenna. I trust the PPP-calculated position accuracy of this receiver to within low double digits to high single digit millimeters. (For comparison, the report from NrCAN gives a 95% error ellipse on the UBlox as semi-major: 2.494dm, semi-minor: 1.760dm. The corresponding numbers for the NetRS is semi-major: 1.245cm, semi-minor: 0.760cm - the reports are usually below 10 mm in both axis. Note difference in units.) Comparing the calculated ECEF coordinates from the ppp-results using Pythagoras gives me a distance of 76 cm - 53 cm if we simply ignore height. This is with a survey grade antenna in a good location. It might be possible to shrink this to 30 cm and still have confidence in the results, but I think it would not be easy. I would guess a lot more data would be required, and it is also possible that delaying processing until more accurate ionospheric maps are available could help. I will reprocess in a couple of days and see if theres much of a difference. Ole On Wed, Apr 25, 2018 at 4:56 PM, Tom Van Baak wrote: > List -- I had a recent query by a researcher who would like to pinpoint > the location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing > requirements as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed > the line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get > after an hour, or even 24 or 48 hours? And here I mean accurate, not > stable. Have any of you compared that self-reported, self-survey result > against an independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help > recommend solution(s) to the researcher's question or shed light on this > interesting challenge. > > Thanks, > /tvb > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi Keep in mind when you look at the “peak to peak” numbers for solid tides that you may have to observe things for 20,000 years to see the full peak to peak…… They also are variable depending on just how close you are to what sort of coastline. ( = they interact with sea tides when you get close). Bob > On Apr 25, 2018, at 3:26 PM, Hal Murray wrote: > > >> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D >> position? > > Elevation gets interesting. Earth has tides in solid rock that are ballpark > of that scale peak-peak. > > It would be interesting to see if you could see the tides with low cost gear. > > > -- > These are my opinions. I hate spam. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
You will probably have a some difficulty finding a surveyor that does geodetic/mm accuracy surveys. Most surveyors that use GPS seem to work down to inches/a few cm. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi Tom, > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > I suspect just L1 would be fine in areas with dense CORS. I have not tried it, but how about this ultra-cheap strategy: 1. obtain L1 observables with a cheap board and cheap patch antenna; convert to RINEX 2. synthesize fake L2 data, using nominal iono conditions, and add it to the RINEX 3. submit to NOAA's rapid static solver, OPUS-RS, which currently accepts only dual-frequency data 4. examine the quality report from OPUS-RS to see if the ambiguities were reliably resolved But this is a bit of a dicey science project; I'd suggest that the researcher borrow a survey receiver for a few days (mild learning curve for the online solver tools) or hire a surveyor (no learning curve). Cheers, Peter ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
It is true that most handheld GPS receivers have WAAS capability these days; however the accuracy is more like 3 to 4 meters even with several minutes of averaging. I've always been puzzled by why it is so much worse than good professional equipment can apparently achieve with similar "features". Perhaps it has something to do with the simple antennas that handheld units use. A day or two ago I had related the story of our survey at the Arecibo observatory done with professional equipment. Soon after that was done, I took my handheld Garmin GPS60CX up on the roof and used it to make the same measurement with WAAS corrections turned on and about 10 min of averaging. I don't remember the exact numbers for the discrepancies between the two measurements, but they were in the neighbor hood of 4 meters. In fairness to the handheld, I should mention that the position involved did not offer complete sky visibility- it was in sort of a canyon such that the sky was visible only down to about 30 or 40 deg elevation to the east and west but with excellent low-elevation visibility to the north and south. Incidentally, Puerto Rico does have a WAAS ground station fairly close to the observatory site, just off the San Juan airport roughly 50 miles away from the observatory. Dana On Wed, Apr 25, 2018 at 8:21 PM, jimlux wrote: > On 4/25/18 11:18 AM, Brooke Clarke wrote: > >> Hi Tom: >> >> As part of a FireWise community mapping process I'd like to get GPS >> coordinates of the fire hydrants (Lat, Lon, Ele). Is there a civilian GPS >> receiver that makes use of WAAS and/or DGPS corrections? >> > > I think almost all handheld receivers these days use WAAS for improved > performance. WAAS should give you 1 meter kind of accuracy, particularly > if you compare a known location in the area. > > DGPS was a thing back in the 90s (I fooled with a Trimble Scout with a pod > that received corrections over FM broadcast SCA) - I'm not sure it's widely > used today. > > The USCG DGPS transmits corrections on MF beacons, but is being > decommissioned. Most of the inland stations have been shutdown. > > > If you're a surveyor, you get corrections from a network (CORS or > something similar), or you're primarily interested in "relative" position - > you set up your base station and your RTK rover tells you where it is > within 1 mm + 1ppm of distance from base. > > http://www.xyht.com/ has regular features on the latest GPS survey gear. > > You might be able to convince the local survey equipment rental house to > come out and demo the gear (or give you a good price on a rental) > > Or, why not just do the survey optically (!) - none of this new fangled > GPS stuff. Rod, level, theodolite. If Everest could do it in the 19th > century in India, you can do it too. > > If you can find a couple benchmarks to work from, you can get accuracy of > 1 part in 1000 with a decent 200 foot tape measure and something to sight > with (a cheap laser level at night works pretty good to keep your line > straight). You're doing a series of triangles - SSS completely defines it, > so no angles need be measured. > > With decent survey gear 1 part in 10,000 or so is straightforward. > > 1 ppm is hot stuff with conventional optical gear - you're going to be > making multiple measurements, compensating for refraction, etc. It's like > GPS at 10cm accuracy - lots of things cause errors of that magnitude. > > A nice theodolite (like a Wild T2) is readable to 1 second of arc. That's > about 5 microradian. At 100 meters, the horizontal uncertainty would be > 0.5mm. Yeah, not quite 1ppm, although you could probably do multiple > setups and average in on 1ppm. > > Of course, you'll then need to go out and get a decent tripod, a rod and > target, and a rod person to wave the rod, etc. > > But another poster did comment on "why not use the telescope" you could > precision point to a series of stars and calculate using celestial nav > where you are. Although, that might be painful to the 1 meter sort of > accuracy - the "tables" probably don't really account for deviations from > ellipsoid and so forth. > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/m > ailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Jim Lux writes: > But another poster did comment on "why not use the telescope" you could > precision point to a series of stars and calculate using celestial nav > where you are. Although, that might be painful to the 1 meter sort of > accuracy - the "tables" probably don't really account for deviations from > ellipsoid and so forth. I took a shot at this recently, using the optical signal available from GPS, Project Echo style: http://fer3.com/arc/m2.aspx/Navigating-with-GPS-optically-PeterMonta-jan-2018-g41217 It would be difficult to get to 0.3 meter, though. More like 15 meter single shot, maybe 5 meter with averaging. As the other responses point out, this is routine for GNSS surveying. A few hours of dual-frequency GPS data is enough for accuracy of a few centimeters. If reference stations such as CORS are available, the "rapid static" solvers cut the needed session time to 20 or 30 minutes. Set up a reference mark in a clear area, get its position, then use a total station to do optical ties to other local marks like the telescope mount. Cheers, Peter ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On 4/25/18 7:46 PM, Brooke Clarke wrote: Hi J: I had a number of survey stakes I placed using a manual transit and tape measure and hired a local surveyor to tell me where they were and also tell me where my GPS antenna was located. He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total station on another tripod and ran a cable between the two. After some time (tens of minutes or ??) he used the theodolite to sight my stakes and the GPS antenna. I got a report back in a week or so. Total cost a few hundred dollars. I'm in the process of looking at how accurate the GPS is in my new LG G6 phone. Yep - A typical total station is good to "a few seconds" (some single digit mm at 100 meters) in angle. Distance is usually pretty accurate 1.5 mm + 2ppm. So over a typical 100m sort of size (several acres) a total station can provide relative positions to better than a cm, but probably not better than a mm. A good optical theodolite can do *maybe* an order of magnitude better, in terms of the basic measurement, but then there's other confounding factors that might dominate. For instance, are you sure you're holding the prism/target *precisely* over the mark? And just what *is* that mark. Precision metrology in any field is fascinating, but a rabbit hole down which one can fall very, very deep. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi J: I had a number of survey stakes I placed using a manual transit and tape measure and hired a local surveyor to tell me where they were and also tell me where my GPS antenna was located. He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total station on another tripod and ran a cable between the two. After some time (tens of minutes or ??) he used the theodolite to sight my stakes and the GPS antenna. I got a report back in a week or so. Total cost a few hundred dollars. I'm in the process of looking at how accurate the GPS is in my new LG G6 phone. -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message I think to really be confident about a position you really need the dual-frequency data (or that data from a nearby reference station), otherwise you could end up in a situation where you're consistent, but that consistency has a bias. IIRC, anyhow -- I'm not sure how the math actually works out. Anyhow, I play around with PPP stuff on occasion, and the last run I did was in November using the Novatel OEM628 kit that was briefly available for cheap on eBay, and the included 702-GG antenna (which, conveniently, has calibrations available). Running a day's worth of data through CSRS-PPP produced sigmas (95%) of 0.004m latitude, 0.008m longitude, and 0.024m in elevation. I've done some shorter runs since then that appear to fall in that same range ... I really need to do a few more full runs and see what kind of variance there is. At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even takes solid earth tides into account, though I didn't do that because I was never able to figure out which specific type of solid earth tide data I needed. I imagine there's still some issues with any given datum being somewhat imperfect, as far as altitude is concerned, and I don't really know how to correctly deal with that if exact altitude matters. Maybe we should all just agree to use XYZ/ECEF coordinates for everything and give up on this whole altitude thing altogether... ;) (As an aside, I've been tempted to get someone to come professionally survey my antenna and tell me where it _actually_ is, so I could see how well I could actually do with my GPS kit, but I imagine it's pretty expensive -- anyone happen to know what getting that kind of thing done actually ends up costing?) -j ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On 4/25/18 11:18 AM, Brooke Clarke wrote: Hi Tom: As part of a FireWise community mapping process I'd like to get GPS coordinates of the fire hydrants (Lat, Lon, Ele). Is there a civilian GPS receiver that makes use of WAAS and/or DGPS corrections? I think almost all handheld receivers these days use WAAS for improved performance. WAAS should give you 1 meter kind of accuracy, particularly if you compare a known location in the area. DGPS was a thing back in the 90s (I fooled with a Trimble Scout with a pod that received corrections over FM broadcast SCA) - I'm not sure it's widely used today. The USCG DGPS transmits corrections on MF beacons, but is being decommissioned. Most of the inland stations have been shutdown. If you're a surveyor, you get corrections from a network (CORS or something similar), or you're primarily interested in "relative" position - you set up your base station and your RTK rover tells you where it is within 1 mm + 1ppm of distance from base. http://www.xyht.com/ has regular features on the latest GPS survey gear. You might be able to convince the local survey equipment rental house to come out and demo the gear (or give you a good price on a rental) Or, why not just do the survey optically (!) - none of this new fangled GPS stuff. Rod, level, theodolite. If Everest could do it in the 19th century in India, you can do it too. If you can find a couple benchmarks to work from, you can get accuracy of 1 part in 1000 with a decent 200 foot tape measure and something to sight with (a cheap laser level at night works pretty good to keep your line straight). You're doing a series of triangles - SSS completely defines it, so no angles need be measured. With decent survey gear 1 part in 10,000 or so is straightforward. 1 ppm is hot stuff with conventional optical gear - you're going to be making multiple measurements, compensating for refraction, etc. It's like GPS at 10cm accuracy - lots of things cause errors of that magnitude. A nice theodolite (like a Wild T2) is readable to 1 second of arc. That's about 5 microradian. At 100 meters, the horizontal uncertainty would be 0.5mm. Yeah, not quite 1ppm, although you could probably do multiple setups and average in on 1ppm. Of course, you'll then need to go out and get a decent tripod, a rod and target, and a rod person to wave the rod, etc. But another poster did comment on "why not use the telescope" you could precision point to a series of stars and calculate using celestial nav where you are. Although, that might be painful to the 1 meter sort of accuracy - the "tables" probably don't really account for deviations from ellipsoid and so forth. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
I think to really be confident about a position you really need the dual-frequency data (or that data from a nearby reference station), otherwise you could end up in a situation where you're consistent, but that consistency has a bias. IIRC, anyhow -- I'm not sure how the math actually works out. Anyhow, I play around with PPP stuff on occasion, and the last run I did was in November using the Novatel OEM628 kit that was briefly available for cheap on eBay, and the included 702-GG antenna (which, conveniently, has calibrations available). Running a day's worth of data through CSRS-PPP produced sigmas (95%) of 0.004m latitude, 0.008m longitude, and 0.024m in elevation. I've done some shorter runs since then that appear to fall in that same range ... I really need to do a few more full runs and see what kind of variance there is. At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even takes solid earth tides into account, though I didn't do that because I was never able to figure out which specific type of solid earth tide data I needed. I imagine there's still some issues with any given datum being somewhat imperfect, as far as altitude is concerned, and I don't really know how to correctly deal with that if exact altitude matters. Maybe we should all just agree to use XYZ/ECEF coordinates for everything and give up on this whole altitude thing altogether... ;) (As an aside, I've been tempted to get someone to come professionally survey my antenna and tell me where it _actually_ is, so I could see how well I could actually do with my GPS kit, but I imagine it's pretty expensive -- anyone happen to know what getting that kind of thing done actually ends up costing?) -j On 4/25/18 8:38 AM, Tim Lister wrote: On Wed, Apr 25, 2018 at 7:56 AM, Tom Van Baak wrote: List -- I had a recent query by a researcher who would like to pinpoint the location of his telescope(s) within 0.3 meters. Also (he must be a true scientist) he wants to do this on-the-cheap. He may have timing requirements as well, but that's another posting. So I toss the GPS question to the group. Surely some of you have crossed the line from precise time to precise location? How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D position? When we run our GPSDO in survey mode how accurate a position do we get after an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have any of you compared that self-reported, self-survey result against an independently measured professional result or known benchmark? Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot accuracy given enough time? If not, what improvement would -T models and RINEX-based web-service post-processing provide? It that's still not close enough to 0.3 m, is one then forced to use more expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to achieve this level of precision? If so, how cheaply can one do this? Or is the learning curve more expensive than just hiring an survey specialist to make a one-time cm-level measurement for you? Something tells me 1 foot accuracy in position is possible and actually easier than 1 ns accuracy in time. I'm hoping some of you can help recommend solution(s) to the researcher's question or shed light on this interesting challenge. Hi Tom, list, as another researcher who is also interested in telescope positions (!) I have done this for personal use at home with a ublox 6T and 53532A antenna to see what I got. I was logging in the UBX binary format with the raw (carrier phase) measurements turned on and then converting it to RINEX and using the NRC's CSRS-PPP online service which is one of the few that will take single frequency L1 only data. The results based on approx. 41.5 hours of data and which were post-processed 21 days later (so that they used the IGS Final products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of 0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal height respectively. I was quite impressed with the results without use of the L2 frequency to correct for the ionosphere etc. Thanks, /tvb Cheers, Tim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
I don't know if you can easily see earth tides with a GPS... the post-processing services usually filter and correct them out. But, Lady Heather v6 can model and plot them (as lat/lon/alt displacements in mm). Also the vertical component of the gravity offset (in ugals) ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? Elevation gets interesting. Earth has tides in solid rock that are ballpark of that scale peak-peak. It would be interesting to see if you could see the tides with low cost gear. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi One of the “interesting features” of the ongoing bridge rebuilding process around here is the destruction of most of the benchmark locations. They were built into the old bridges and went away when the new ones went up. Now there are cute little brass disks on the new bridges. There is no information on the disk and no obvious plan to generate that data ….. When one asks about it, the answer is: “nobody does it that way anymore”. Bob > On Apr 25, 2018, at 1:07 PM, Dan Kemppainen wrote: > > Hi, > > Anecdotal response. > > A few years back we played with using handheld garmin units (GPSMAP 62st) for > locating property lines and corners. We averaged for 6 to 12 hours at known > standards (section corners). This data was used to subdivide the section for > property corner locations, and these corners were marked. > > The method for marking was to park the GPS close to the calculated corner > location in Lat/Lon. Then we let the GPS survey for the same 6-12 hour > period, corrected the GPS position and repeated until the desired corner was > located. > > A year or two later due to a power line upgrade, many of the properties were > surveyed professionally. We're in a small community and we got chatting with > the surveyors. We helped them find roads/trails to get to section corners > they needed to get to. They in turn helped us by marking the property corners > in question with survey grade equipment (They said accurate to within an > inch). The handheld GPS units were within about a foot or so of the > professional units. > > Obvious concerns aside, what we were really doing was dividing relatively > short distances (1 mile) between existing point into even shorter distances > between the points. The limiting factor was really number of digits in the > average reported Lat/Lon positions from the GPS. > > That said, with a few good reference points (section corners, or other > standards) near the telescope and some time using a good handheld GPS and > some careful math you should be able to drill down close to 0.3m level of > accuracy. > > We did want to repeat the tests with timing mode receivers set to average for > 48 hours, but haven't got around to it yet. > > Dan > > > > > > > On 4/25/2018 12:00 PM, time-nuts-requ...@febo.com wrote: >> Message: 6 >> Date: Wed, 25 Apr 2018 07:56:14 -0700 >> From: "Tom Van Baak" >> To: "Discussion of precise time and frequency measurement" >> >> Subject: [time-nuts] nuts about position >> Message-ID: <2E0CF8A1D3C64D58BA771539C620ABE9@pc52> >> Content-Type: text/plain;charset="iso-8859-1" >> List -- I had a recent query by a researcher who would like to pinpoint the >> location of his telescope(s) within 0.3 meters. Also (he must be a true >> scientist) he wants to do this on-the-cheap. He may have timing requirements >> as well, but that's another posting. >> So I toss the GPS question to the group. Surely some of you have crossed the >> line from precise time to precise location? >> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D >> position? >> When we run our GPSDO in survey mode how accurate a position do we get after >> an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have >> any of you compared that self-reported, self-survey result against an >> independently measured professional result or known benchmark? >> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot >> accuracy given enough time? >> If not, what improvement would -T models and RINEX-based web-service >> post-processing provide? >> It that's still not close enough to 0.3 m, is one then forced to use more >> expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to >> achieve this level of precision? If so, how cheaply can one do this? Or is >> the learning curve more expensive than just hiring an survey specialist to >> make a one-time cm-level measurement for you? >> Something tells me 1 foot accuracy in position is possible and actually >> easier than 1 ns accuracy in time. I'm hoping some of you can help recommend >> solution(s) to the researcher's question or shed light on this interesting >> challenge. >> Thanks, >> /tvb > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi Tom: I have a friend who bought a house on a hill so that he could build an observatory with an excellent view of the sky. The telescope mount is the Paramount by Software Bisque. This mount is capable of pointing accuracy measured in a small number of arc seconds. That implies the control software knows the time to a high precision. But there's no "time nuts" clock involved. The control PC computer only has the stock NTP function turned on the in the clock. To get that pointing accuracy he uses TPoint software that models the mechanical errors in the mount. As part of the start up procedure he points to a know star or stars and that sets the clock. I expect that the location of the telescope is determined as part of the TPoint alignment process that looks at a large number of stars. PS We used the gun laying function of the DAGR GPS receiver when laying out the observatory to get a North-South line. http://prc68.com/I/DAGR.shtml#GLS As part of a FireWise community mapping process I'd like to get GPS coordinates of the fire hydrants (Lat, Lon, Ele). Is there a civilian GPS receiver that makes use of WAAS and/or DGPS corrections? -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html Original Message List -- I had a recent query by a researcher who would like to pinpoint the location of his telescope(s) within 0.3 meters. Also (he must be a true scientist) he wants to do this on-the-cheap. He may have timing requirements as well, but that's another posting. So I toss the GPS question to the group. Surely some of you have crossed the line from precise time to precise location? How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D position? When we run our GPSDO in survey mode how accurate a position do we get after an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have any of you compared that self-reported, self-survey result against an independently measured professional result or known benchmark? Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot accuracy given enough time? If not, what improvement would -T models and RINEX-based web-service post-processing provide? It that's still not close enough to 0.3 m, is one then forced to use more expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to achieve this level of precision? If so, how cheaply can one do this? Or is the learning curve more expensive than just hiring an survey specialist to make a one-time cm-level measurement for you? Something tells me 1 foot accuracy in position is possible and actually easier than 1 ns accuracy in time. I'm hoping some of you can help recommend solution(s) to the researcher's question or shed light on this interesting challenge. Thanks, /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi,
Anecdotal response.
A few years back we played with using handheld garmin units (GPSMAP
62st) for locating property lines and corners. We averaged for 6 to 12
hours at known standards (section corners). This data was used to
subdivide the section for property corner locations, and these corners
were marked.
The method for marking was to park the GPS close to the calculated
corner location in Lat/Lon. Then we let the GPS survey for the same 6-12
hour period, corrected the GPS position and repeated until the desired
corner was located.
A year or two later due to a power line upgrade, many of the properties
were surveyed professionally. We're in a small community and we got
chatting with the surveyors. We helped them find roads/trails to get to
section corners they needed to get to. They in turn helped us by marking
the property corners in question with survey grade equipment (They said
accurate to within an inch). The handheld GPS units were within about a
foot or so of the professional units.
Obvious concerns aside, what we were really doing was dividing
relatively short distances (1 mile) between existing point into even
shorter distances between the points. The limiting factor was really
number of digits in the average reported Lat/Lon positions from the GPS.
That said, with a few good reference points (section corners, or other
standards) near the telescope and some time using a good handheld GPS
and some careful math you should be able to drill down close to 0.3m
level of accuracy.
We did want to repeat the tests with timing mode receivers set to
average for 48 hours, but haven't got around to it yet.
Dan
On 4/25/2018 12:00 PM, time-nuts-requ...@febo.com wrote:
Message: 6
Date: Wed, 25 Apr 2018 07:56:14 -0700
From: "Tom Van Baak"
To: "Discussion of precise time and frequency measurement"
Subject: [time-nuts] nuts about position
Message-ID: <2E0CF8A1D3C64D58BA771539C620ABE9@pc52>
Content-Type: text/plain; charset="iso-8859-1"
List -- I had a recent query by a researcher who would like to pinpoint the
location of his telescope(s) within 0.3 meters. Also (he must be a true
scientist) he wants to do this on-the-cheap. He may have timing requirements as
well, but that's another posting.
So I toss the GPS question to the group. Surely some of you have crossed the
line from precise time to precise location?
How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D position?
When we run our GPSDO in survey mode how accurate a position do we get after an
hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have any of
you compared that self-reported, self-survey result against an independently
measured professional result or known benchmark?
Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot
accuracy given enough time?
If not, what improvement would -T models and RINEX-based web-service
post-processing provide?
It that's still not close enough to 0.3 m, is one then forced to use more
expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to
achieve this level of precision? If so, how cheaply can one do this? Or is the
learning curve more expensive than just hiring an survey specialist to make a
one-time cm-level measurement for you?
Something tells me 1 foot accuracy in position is possible and actually easier
than 1 ns accuracy in time. I'm hoping some of you can help recommend
solution(s) to the researcher's question or shed light on this interesting
challenge.
Thanks,
/tvb
___
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Re: [time-nuts] nuts about position
This link seems to provide an overview of Differential GPS and some related techniques. https://www.e-education.psu.edu/geog862/node/1834 Building a system along these lines from "auction site purchases" and home brewed computer code might be a fun project but one would presumably need an accurately surveyed starting point. Mark Spencer m...@alignedsolutions.com 604 762 4099 > On Apr 25, 2018, at 8:06 AM, George Watson wrote: > > Create your own DGPS? > > Trimble is good at this. > > George K. Watson > K0IW > >> On Apr 25, 2018, at 10:56 AM, Tom Van Baak wrote: >> >> List -- I had a recent query by a researcher who would like to pinpoint the >> location of his telescope(s) within 0.3 meters. Also (he must be a true >> scientist) he wants to do this on-the-cheap. He may have timing requirements >> as well, but that's another posting. >> >> So I toss the GPS question to the group. Surely some of you have crossed the >> line from precise time to precise location? >> >> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D >> position? >> >> When we run our GPSDO in survey mode how accurate a position do we get after >> an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have >> any of you compared that self-reported, self-survey result against an >> independently measured professional result or known benchmark? >> >> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot >> accuracy given enough time? >> >> If not, what improvement would -T models and RINEX-based web-service >> post-processing provide? >> >> It that's still not close enough to 0.3 m, is one then forced to use more >> expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to >> achieve this level of precision? If so, how cheaply can one do this? Or is >> the learning curve more expensive than just hiring an survey specialist to >> make a one-time cm-level measurement for you? >> >> Something tells me 1 foot accuracy in position is possible and actually >> easier than 1 ns accuracy in time. I'm hoping some of you can help recommend >> solution(s) to the researcher's question or shed light on this interesting >> challenge. >> >> Thanks, >> /tvb >> >> ___ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Hi That sort of accuracy is pretty normal for a survey device. He needs to find a local surveyor who likes to look at stars :). I assume the telescope is not mobile and it’s a one time sort of thing. If he likes to romp around the question becomes how quickly he needs the location information. Post processing is very much part of getting this done. That takes a while (like days .. weeks … months). Bob > On Apr 25, 2018, at 10:56 AM, Tom Van Baak wrote: > > List -- I had a recent query by a researcher who would like to pinpoint the > location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing requirements > as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed the > line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get after > an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have > any of you compared that self-reported, self-survey result against an > independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help recommend > solution(s) to the researcher's question or shed light on this interesting > challenge. > > Thanks, > /tvb > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
On Wed, Apr 25, 2018 at 7:56 AM, Tom Van Baak wrote: > List -- I had a recent query by a researcher who would like to pinpoint the > location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing requirements > as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed the > line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get after > an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have > any of you compared that self-reported, self-survey result against an > independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help recommend > solution(s) to the researcher's question or shed light on this interesting > challenge. Hi Tom, list, as another researcher who is also interested in telescope positions (!) I have done this for personal use at home with a ublox 6T and 53532A antenna to see what I got. I was logging in the UBX binary format with the raw (carrier phase) measurements turned on and then converting it to RINEX and using the NRC's CSRS-PPP online service which is one of the few that will take single frequency L1 only data. The results based on approx. 41.5 hours of data and which were post-processed 21 days later (so that they used the IGS Final products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of 0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal height respectively. I was quite impressed with the results without use of the L2 frequency to correct for the ionosphere etc. > > Thanks, > /tvb > Cheers, Tim ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
While I was at the Arecibo Observatory it became desirable to get a good surveyed position for a new GPS antenna we had installed for the NIST TMAS system. We found a resource at the Univ of Puerto Rico who had a Trimble (I think) unit. He set it up on the site, "turned on the bubble machine", then left it alone for about two hours. He returned the estimated position a few days later, expressing high confidence that it was good within about 8 inches. I'm sure I asked him if this machine used both L1 & L2, but don't recall his answer. I suspect it was "yes". Dana On Wed, Apr 25, 2018 at 9:56 AM, Tom Van Baak wrote: > List -- I had a recent query by a researcher who would like to pinpoint > the location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing > requirements as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed > the line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get > after an hour, or even 24 or 48 hours? And here I mean accurate, not > stable. Have any of you compared that self-reported, self-survey result > against an independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help > recommend solution(s) to the researcher's question or shed light on this > interesting challenge. > > Thanks, > /tvb > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
When in was developing Lady Heather's precision survey code I was comparing the calculated positions to those from an Ashtech Z12 dual freq GPS (with the position calculated by OPUS). Using the same survey grade antenna and a Thunderbolt the results were usually within a meter. I have not tried it using a more modern GPS receiver. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] nuts about position
Create your own DGPS? Trimble is good at this. George K. Watson K0IW > On Apr 25, 2018, at 10:56 AM, Tom Van Baak wrote: > > List -- I had a recent query by a researcher who would like to pinpoint the > location of his telescope(s) within 0.3 meters. Also (he must be a true > scientist) he wants to do this on-the-cheap. He may have timing requirements > as well, but that's another posting. > > So I toss the GPS question to the group. Surely some of you have crossed the > line from precise time to precise location? > > How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D > position? > > When we run our GPSDO in survey mode how accurate a position do we get after > an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have > any of you compared that self-reported, self-survey result against an > independently measured professional result or known benchmark? > > Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot > accuracy given enough time? > > If not, what improvement would -T models and RINEX-based web-service > post-processing provide? > > It that's still not close enough to 0.3 m, is one then forced to use more > expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to > achieve this level of precision? If so, how cheaply can one do this? Or is > the learning curve more expensive than just hiring an survey specialist to > make a one-time cm-level measurement for you? > > Something tells me 1 foot accuracy in position is possible and actually > easier than 1 ns accuracy in time. I'm hoping some of you can help recommend > solution(s) to the researcher's question or shed light on this interesting > challenge. > > Thanks, > /tvb > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] nuts about position
List -- I had a recent query by a researcher who would like to pinpoint the location of his telescope(s) within 0.3 meters. Also (he must be a true scientist) he wants to do this on-the-cheap. He may have timing requirements as well, but that's another posting. So I toss the GPS question to the group. Surely some of you have crossed the line from precise time to precise location? How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D position? When we run our GPSDO in survey mode how accurate a position do we get after an hour, or even 24 or 48 hours? And here I mean accurate, not stable. Have any of you compared that self-reported, self-survey result against an independently measured professional result or known benchmark? Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot accuracy given enough time? If not, what improvement would -T models and RINEX-based web-service post-processing provide? It that's still not close enough to 0.3 m, is one then forced to use more expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to achieve this level of precision? If so, how cheaply can one do this? Or is the learning curve more expensive than just hiring an survey specialist to make a one-time cm-level measurement for you? Something tells me 1 foot accuracy in position is possible and actually easier than 1 ns accuracy in time. I'm hoping some of you can help recommend solution(s) to the researcher's question or shed light on this interesting challenge. Thanks, /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
