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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: GPS as a time authority
From: Richard B. Langley
Date: 2009 Sep 15, 14:14 -0300
From: Richard B. Langley
Date: 2009 Sep 15, 14:14 -0300
All these references to a GPS receiver knowing UT1, should say UTC. Granted, the difference between UT1 and UTC is never as large as 0.9 seconds, but there is a difference. The GPS navigation message contains the current offset between GPS (System) Time and UTC as well as advance notice of upcoming leap seconds when they are announced. -- Richard Langley Quoting Lu Abel: > > Antoine: > > Most GPS receivers are, however, aware of the difference between "GPS > time" and UT1 and automatically correct for it in their display. If > one digs down down into the setup parameters in the average GPS receiver > one will find a choice of time displays, including both GPS time and > UT1. The factory default setting is usually UT1, since that is the > time we all live by. > > But you do raise an interesting point -- is it possible that the time > difference observed by the original poster, John Parsons, was due to > someone having their GPS set to display GPS time rather than UT1??? > > Lu Abel > > antoine.m.couette@club-internet.fr wrote: > > I think that the reason brought up by "M. Lunav" is quite valid : processing times > may vary according to types of GPS receivers. > > > > There is also an ESSENTIAL REASON, which may have been skipped in this thread. > > > > GPS cannot accomodate any time discontinuities. Therefore, some 15 years ago, GPS > time - i.e. the one used by the GPS System - was the same as UT1. > > > > Now with the extra seconds added now and then to take in account the Earth rotation > changes, GPS time itself which is much more stable than UT1 has become different from > UT1 by a number of seconds amounting to 8 seconds (this amount to be confirmed) > to-day. > > > > Antoine M. Cou?tte > > > > > > > > > > > > > =============================================================================== Richard B. Langley E-mail: lang@unb.ca Geodetic Research Laboratory Web: http://www.unb.ca/GGE/ Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142 University of New Brunswick Fax: +1 506 453-4943 Fredericton, N.B., Canada E3B 5A3 Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/ =============================================================================== --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---