Re: Coordinates of AIS targets

[Andreas B]

If you need AIS-data for testing, check out
https://www.kystverket.no/en/navigation-and-monitoring/ais/access-to-ais-data/.
There is a live stream of AIS provided on ip:port; 153.44.253.27:5631.

Best regards,
Andreas

On Mon, May 8, 2023 at 11:11 PM Gary E. Miller <gem@rellim.com> wrote:
>
> Yo Владимир!
>
> On Mon, 8 May 2023 20:09:56 +0300
> Владимир Калачихин <v.kalachikhin@gmail.com> wrote:
>
> > 07.05.2023 22:29, Gary E. Miller пишет:
> > >> the OpenCPN and SignalK understands my AIS sentences and display
> > >> targets in correct coordinates, but gpsd not.
> > > Odd, I'd need to see your raw AIS to make a gues.
> > >
> >
> > I found that coordinates in 27'th sentence rounded to one decimal
> > place. But for 18'th sentence the accuracy is maintained.
>
> I looked at the standard:
>
> https://www.itu.int/rec/R-REC-M.1371/en
>
> The transmitted message 18 precision is 1/600,000th of a degree
> (0.00000166...)  Message 18 output format for lat/lon was %.6f.  I
> bumped that up to %0.7f to maintain precision.
>
> > The coordinates are stored in 27'th sentence with precision of 1/600
> > of degrees, so gpsd must return it as least with two decimal places
> > precision.
>
> Per M.1371:
>
> 1/10 minute, which is 1/000 degrees.  So I made that %.4f.
>
> The transmitted message 27 precision is 1/600th of a degree (0.00166..).
> It was %.1f in gpsd, I changed that to %.4f.
>
> I also adjusted some of the other lat/lon message's precisions.
>
> > In attachment the AIS flow with 27 and 24 sentences only.
>
> 18 and 27 only.
>
> Is that different than you last one?  If so, how?  Which is best to
> use?
>
> I always prefer untouched captures.  For best test coverage.
>
> > The
> > coordinates in 27 sentence has full precision.
> > I try:
> > $ gpsfake digitrafficAIS27Y.log
> > and in other terminal:
> > $ gpspipe -w --scaled
>
> Easier: gpsdecode < digitrafficAIS27Y.log
>
> Changes pushed.  Please test.  I also added your digitrafficAIS.log as
> a regression test, but would prefer a full, unedited, log.
>
> RGDS
> GARY
> ---------------------------------------------------------------------------
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
>         gem@rellim.com  Tel:+1 541 382 8588
>
>             Veritas liberabit vos. -- Quid est veritas?
>     "If you can't measure it, you can't improve it." - Lord Kelvin