NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: GPS as a time authority
From: Lu Abel
Date: 2009 Sep 15, 10:18 -0700
From: Lu Abel
Date: 2009 Sep 15, 10:18 -0700
Thanks for the correction, Richard. I should have used the correct
terminology.
Lu
Richard B. Langley wrote:
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Lu
Richard B. Langley wrote:
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 <lunav@abelhome.net>: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 timesmay 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, GPStime - 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 rotationchanges, 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/ ===============================================================================
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