for those who really want to know, look at: http://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System
There are a lot of 'urban myths' around the GPS, make sure your information is verified. Leslie. I did not study it, but have friends who use GPS to sub-centimeter accuracy... -------------------------------------------- On Sat, 12/6/14, Rick Brass via CnC-List <cnc-list@cnc-list.com> wrote: Subject: Re: Stus-List Navigation To: "'Dennis C.'" <capt...@gmail.com>, cnc-list@cnc-list.com Date: Saturday, December 6, 2014, 6:58 PM 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 BrassWashington, 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 #83Mandeville, LA Currently on the hook at30 23.054N 86 51.884W Sent from my iPhone -----Inline Attachment Follows----- _______________________________________________ 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
