Re: [gpsd-dev] Parallel build broken?

[Gary E. Miller]

Yo Paul!

On Mon, 25 Nov 2013 12:20:26 +0400
Paul Fertser <address@hidden> wrote:

> Hi,
> 
> On Sun, Nov 24, 2013 at 11:39:35PM -0800, Gary E. Miller wrote:
> > Paul Fertser <address@hidden> wrote:
> > > One possible universal measure would be to mark the time as
> > > inaccurate until after, say, 25 minutes (2x full almanac
> > > transmission interval to improve robustness) 
> > > doesn't require knowing current GPS-UTC value at all.
> > 
> > 2x a full almanac is 4 hours.  Some parts of the almanac are only
> > sent once every two hours.
> 
> [1] (listed as a reference on Wikipedia) disagrees (quote from
> wikipedia, the content matches [1] but is more condensed):

Always best to check the the core document for GPS: IS-GPS-200E.pdf.
Every generation you get away from that errors creep in.  Wikipedia good
for an overview, but even they say is never canonical.

If we are going to get really technical, then yes "almanac" is sent
every 12.5 minutes, but the almanac is not what we want.  As the spec
says: 20.3.3.5.2.1 "The almanac is a subset of the clock and ephemeris
data, with reduced precision."  So you really want the ephemeris, not
the almanac.  And the ephemeris needs two hours:

30.3.3.1.1 "The ephemeris parameters in the message type 10 and type 11
describe the orbit of the transmitting SV during the curve fit interval
of three hours. The nominal transmission interval is two hours, and
shall coincide with the first two hours of the curve fit interval."



RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701
        address@hidden  Tel:+1(541)382-8588

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