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Re: [gpsd-users] Status of my patches.

From: Gary E. Miller
Subject: Re: [gpsd-users] Status of my patches.
Date: Sat, 1 Sep 2018 16:22:09 -0700

Yo Sven!

On Sat, 1 Sep 2018 11:32:42 +0000 (UTC)
Sven Geggus <address@hidden> wrote:

> The currunt code uses %.4f which means roughly 11.11meters

Yeah, that is a bit too sloppy.  That makes it clear that %.5f is
the way to go currently.

> This said I strongly feel that the reference here should not be the
> accouracy of current GPS which may well get better in future but the
> full resolution the encoding (NMEA) actually provides.

If we only had a copy of the NMEA spec...

> According to the documentation ( NMEA
> encoding in AIS messages provides a resolution of minutes/10000.

Well, proving something to the gpsd project, by citing the gpsd docs,
is a bit circular.  More important is if we have real world captures
from live hardware showing that precision.

> Conclusion: To represent GPS accuracy use at least %.45f to represent
> resolution of NMEA rencoding use %.6f

Some NMEA, not all.  NMEA is all over the map.  But since some cheap
GPS can now almost get to 1m (%.5f) it seems that 0.1m (%.6f) is only
somewhat overkill.  Just don't believe that last digit, and the
next to last digit is pretty marginal.

Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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