Re: course of AIS targets

[Gary E. Miller]

Yo Владимир!

On Fri, 19 May 2023 23:31:40 +0300
Владимир Калачихин <v.kalachikhin@gmail.com> wrote:

> gpsd: 3.22 in scaled mode.

gpsd version 3.25 is the released version.  The patches to your previous
issues are in git head.  3.22 is almost 3 years old.  Please move your
testing to git head.

> Message 1: The COG value == 3600 interpreted by gpsd as 360, but not 
> null. https://www.navcen.uscg.gov/ais-class-a-reports

JSON does not support "null".  In JSON, numeric values MUST be numeric.
Only.

> It is a bug.

Nope.  As the AIS spec says:

    Latitude in 1/10 000 min (±90°, North = positive (as per 2’s
    complement), South = negative (as per 2’s complement). 91°
    (3412140h) = not available = default)

Since JSON has no "null" value, and numerics must be numeric, it is normal
to follow the spec and use 360.0 as "not available".  Exactly as the spec
says to do.

If you prefer, since the COG is "not available", I could change gpsd_json.c
sp that when 360.0 == COG, to not output the field at all.  Would you
prefer that.

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

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