Re: Coordinates of AIS targets

[Gary E. Miller]

Yo Владимир!

On Thu, 11 May 2023 11:09:48 +0300
Владимир Калачихин <v.kalachikhin@gmail.com> wrote:

> 09.05.2023 21:12, Gary E. Miller пишет:
> > Of course it is best when someone that knows AIS points me to gpsd
> > bugs in AIS.  
> 
> I'm not well in AIS, but I view that gpsd strange in AIS data
> presentation. So,

AIS not my thing either.

I do not consider JSON to be "presentation" layer.  It is "data interchange"
layer, not meant for direct human consumtpion.

> in 'scaled' mode:
> 
> The draught from 24'th sentence represented in meters instead of 
> decimeters in AIS. This is such in TPV and it is expected.
> But the draught from 8'th sentence represented in sentimeters, such
> it in AIS. This is unexpected.

Everyone has different expectations.  I try not to have expectations, but
instead use the doc.  This is documented in "man gpsd_json":  Much
better if all JSON distances are in meters.  To reduce the need to keep
checking the gpsd documentation.

"Vessel draughts are converted to decimal meters rather than native AIS
decimeters."

Way too late to change it, it would create bug reports for a decade.

> Speed, length and beam left in AIS units but coordinates and course 
> brought to the normal form.

Uh, what is "normal form"?  All I care is that the code performs as the
gpsd documentation says it does.

> Values  meaning "no value" in AIS are everywhere, instead null value.

Sadly, JSON does not support "null".  If you have particular ones to look
at, then please be very specific.

> I understand that it can't be changed now, but can it be documented?

I agree that "man gpsd_json" could say more about AIS.  If you have a
text improvement, please send it along.

RGDS
GARY
---------------------------------------------------------------------------
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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    "If you can't measure it, you can't improve it." - Lord Kelvin

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