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

[Gary E. Miller]

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 (http://catb.org/gpsd/AIVDM.html) 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.

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

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