On Wed, 24 May 2017, Pete Biggs wrote:
The GPS time system is also notoriously very precisely wrong. The time was set when the first satellite was sent up and has never been corrected since - so hasn't taken account of leap seconds or relativistic effects. All that matters for GPS is that the time on each satellite transmission is identical, and to that end you can get a precision of about 3ns (which is what you need to get metre GPS accuracy) and which you then have to correct for all the various artefacts since inception. Lower cost GPS receivers get about 50ns accuracy, which is probably still OK for a system clock. The good thing is that the corrections necessary are well known and updated frequently.
http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html https://www.aapt.org/doorway/TGRU/articles/Ashbyarticle.pdf http://www.timetoolsglobal.com/information/gps-ntp-server/ I'll accept that it doesn't include leap seconds, but it does provide the offset from GPS time to UTC, so that's not an issue. I understand the exact opposite as far as relativistic effects, with countering them being necessary for it to work as a positioning system. jh _______________________________________________ CentOS mailing list CentOS@centos.org https://lists.centos.org/mailman/listinfo/centos
