Date: Thu, 04 May 2000 01:02:29 -0600 From: Wes Peters <wes@softweyr.com> To: Warner Losh <imp@village.org> Cc: Matthew Dillon <dillon@apollo.backplane.com>, hackers@FreeBSD.ORG Subject: Re: GPS heads up Message-ID: <39112085.DD0E6502@softweyr.com> References: <200005040303.UAA66590@apollo.backplane.com> <200005032313.QAA65552@apollo.backplane.com> <200005031744.KAA63550@apollo.backplane.com> <20000503200006.A35116@cichlids.cichlids.com> <200005031957.NAA01354@nomad.yogotech.com> <20000503130759.A15403@orion.ac.hmc.edu> <20000503221528.A37472@cichlids.cichlids.com> <20000503151513.D337@beastie.localdomain> <200005040230.UAA36034@harmony.village.org> <200005040321.VAA36306@harmony.village.org>
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Warner Losh wrote:
>
> What I was trying to say was that SA is caused by the satellites
> reporting times that have a small offset added to or subtracted from
> them. Knowing where you are requires that you know what time it is to
> a very precise degree. Once you know what time it is, you can know
> where you are. That's why SA injects a pseudo random noise factor
> into the timing information that the satellites report. If you have
> an atomic clock and a GPS clock, you can measure the offset between
> the two fairly easily and graph the results. That is what I mean when
> I say you can compensate for the SA if you have a good atomic clock.
This is what "Differential GPS" provides: a standard time source that
can be used to remove the SA meanderings from the GPS fix.
--
"Where am I, and what am I doing in this handbasket?"
Wes Peters Softweyr LLC
wes@softweyr.com http://softweyr.com/
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