Sorry guys, but you are talking about the status quo from a few years back. The US military (who is administering the GPS system) initially introduced an intentional 30 m inaccuracy, but it was lifted a long time ago (2000 ??).
The WAAS was introduced to compensate for that error (by Coast Guard?), but it applies mostly to the US coasts. Additionally WAAS requires a good quality signal from one of the three satellites that support it (geo-stationary; 46, 48 and 51). It also uses much more of the radio power so in some application, it affects the battery use. If you have good view of the sky, the WAAS does not, usually, help much in lowering the error of position (10-30 ft; 3-9 m) Additionally, the relativistic time slowing time issue has been resolved a long time ago, as well. If I remember correctly very early after the system was launched. The problem is still talked about, because initially, it was thought, that the relativistic errors would not be that big (but they turned out to be quite significant). The satellite clocks are corrected for that (they tick a bit (;-) faster). One of the biggest issue is that even if your position is showing in the middle of the position circle, it can be anywhere within that circle. And the position accuracy depends on the quality of signal at the given point (of time and space). One needs to keep in mind that the errors can easily creep in from many signal interferences. And another keep in mind thing is that on occasion some of the satellites go out of service (e.g. for maintenance or for military training or other use). I have seen on many occasions notices that the GPS system would not provide accurate information from <date/time> to <date/time>. If you want an accurate position, you may want to invest in a system similar to what America’s Cup was using during the last races. They managed to have the position defined down to 10 cm (if I recall correctly). But you won’t get it from any of the systems that any of us might even consider for our sailboats (unless you are willing to spend more on your GPS receiver than on your boat, including 20 years of maintenance and exploitation costs (;-)). Btw. some of the newer GPS receivers are now using a 10 Hz (instead of 1 Hz) receivers. This substantially increases the accuracy, especially if you are moving. Marek (in very cold Ottawa) From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Dan via CnC-List Sent: Saturday, December 06, 2014 10:57 PM To: Chuck S; cnc-list@cnc-list.com Subject: Re: Stus-List Navigation if you are using a WAAS enabled GPS - the accuracy is as good as military - it compensates for the offset. Sent from my iPhone On Dec 6, 2014, at 19:34, Chuck S via CnC-List <cnc-list@cnc-list.com> wrote: Joel, I've heard this argument years ago, that the gov't intentionally altered the GPS signal. I really think the system is not being jambed, but the number of satelites connected could be limited. I think it's more to control bandwidth than to intentially confuse non-military users. Don't think they want us to run off course and have to dispatch more resources like coast guard helicopters to rescue boater Chuck Resolute 1990 C&C 34R Broad Creek, Magothy River, Md _____ From: "CNC boat owners, cnc-list" <cnc-list@cnc-list.com> To: "Rick Brass" <rickbr...@earthlink.net>, "CNC boat owners, cnc-list" <cnc-list@cnc-list.com> Sent: Saturday, December 6, 2014 10:18:58 PM Subject: Re: Stus-List Navigation Civilian GPS equipment is intentionally less accurate than military equipment. Your government doesn't want you to know exactly where you are! Joel On Saturday, December 6, 2014, Rick Brass via CnC-List <cnc-list@cnc-list.com> wrote: Hope you are having a great, and warm, weekend, Dennis. It is rainy, gray, and the high was about 60 in NC today. Not a nice day for boating. We have all experienced the sort of GPS errors you mentioned at one time or another. And because we all know that our GPS receiver can calculate out position to an accuracy of 30 feet or so, we tend to think that the charts are wrong. But that might not be the whole truth. I’d bet NOAA had pretty good GPS location numbers on the buoys you “hit”, and is not far off on the position of the seawall. The 10 to 30 foot accuracy our GPS reports is based on things like the number and position of the satellites from which it is getting signals, allowing for things like the accuracy of its internal clock, inaccuracy in the chart datum, and the radio waves that carry the time signals from the satellites getting “bent” by the Earth’s magnetic field. But there is another variable that the GPS can’t allow for. I remember reading, a few years ago, about the GPS system in one of the science magazines aimed at geeks like me (Probably Scientific American or Air and Space, but I can’t recall for sure). Seems the GPS system is a good example of Einstein’s Theory of Relativity. Part of the theory says that when you go faster, time slows down relative to time measured in a location that is moving more slowly. The GPS satellites are traveling at something like 18000MPH faster than we are on the Earth’s surface. So the atomic clocks on the satellites “tick” just a wee bit more slowly than the clock on earth. There is a government facility outside of Omaha where military personnel are tasked with adjusting the clocks on the satellites, by a few microseconds or nanoseconds, several times per day to maintain the accuracy of the time signals relative to the earthbound time. As I recall, if the clocks were not adjusted for 24 hours, the calculated position of a spot on Earth would be off by something like 5 miles. That’s probably more than you wanted to know. But you can probably chalk up all those buoys the chartplotter boat ran into to Albert. Oh, and another bit of Einstein trivia: He issued the original patents for the recipe for Tolberone Chocolate, and the shape of the candy. Which is not boating related, unless your Admiral likes really good chocolate. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Dennis C. via CnC-List Sent: Monday, December 01, 2014 8:48 AM To: Della Barba, Joe; cnc-list@cnc-list.com Subject: Re: Stus-List Navigation I was motoring up a harbor looking at a nice Raymarine system showing the boat going through a sea wall 200 feet west of our actual position. Yesterday while motoring in the ICW channel in Santa Rosa Sound near Navarre, FL, the chartplotter boat took out several of the buoys on the right side of the channel. Dennis C. Touché 35-1 #83 Mandeville, LA Currently on the hook at 30 23.054N 86 51.884W Sent from my iPhone -- Joel 301 541 8551 _______________________________________________ This List is provided by the C&C Photo Album Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com _______________________________________________ This List is provided by the C&C Photo Album Email address: CnC-List@cnc-list.com To change your list preferences, including unsubscribing -- go bottom of page at: http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com
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