From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from snark.thyrsus.com (static-71-162-243-5.phlapa.fios.verizon.net [71.162.243.5]) by huchra.bufferbloat.net (Postfix) with ESMTP id A4EE3200B29 for ; Sun, 6 May 2012 14:29:17 -0700 (PDT) Received: by snark.thyrsus.com (Postfix, from userid 1000) id A2B0B40475; Sun, 6 May 2012 17:28:43 -0400 (EDT) Date: Sun, 6 May 2012 17:28:43 -0400 From: "Eric S. Raymond" To: Hal Murray Message-ID: <20120506212843.GA14699@thyrsus.com> References: <20120502033345.GA11913@thyrsus.com> <20120502075808.6CC7880003B@ip-64-139-1-69.sjc.megapath.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120502075808.6CC7880003B@ip-64-139-1-69.sjc.megapath.net> Organization: Eric Conspiracy Secret Labs X-Eric-Conspiracy: There is no conspiracy User-Agent: Mutt/1.5.21 (2010-09-15) Cc: thumbgps-devel@lists.bufferbloat.net, gpsd-dev@nongnu.org Subject: Re: [Thumbgps-devel] [gpsd-dev] PPS over USB X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list Reply-To: esr@thyrsus.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 06 May 2012 21:29:18 -0000 Hal Murray : > > esr@thyrsus.com said: > > Clock time should be OK even with a single sat - multiple birds are needed > > for the spherical trig to compute position, but atomic time you get directly > > from each sat sample. > > I think it's more complicated than that. > > You can get time with only 1 sat if know where you are located. It takes > special software, usually called "timing". That's if you care about precision to less than the variation in lightspeed-from-orbit and ionosphere delays. Physicists do; most other people don't, which is why uBlox can sell a device with a time-service mode that (as I read the datasheet) doesn't require a pre-survey. Theoretical discussion only, since most GPses won't report time without a (3-sat) fix and GPSD doesn't > It's worth asking Navisys if they have the timing mode software. No chance. I can ask, but I'm certain they'll not evenn know it exists. -- Eric S. Raymond