Re: [gpsd-dev] ABVDM sentences from AIS

[Eric S. Raymond]

Iván Sánchez Ortega <address@hidden>:
> A bit of background: "AIVDM" is split into the "Talker ID" ("AI") and the 
> "Sentence formatter" ("VDM"/"VDO"). An "AI" talker is a "Mobile AIS station" 
> (a boat), and "BS" is a "Base Station" (big antenna on ground).

I actually somehow managed not to know this, though I see BS is
supported in gpsd's lexer.  Where are AIS talker IDs documented?  I'd
like to summarize them in my AIVDM/AIVDO protocol decoding guide.

> As far as I'm aware, with the introduction of NMEA 4.00 the talker ID "BS" 
> will disappear and will be replaced by either "AB" or "AD" and maybe "AT" and 
> "SA", plus there will be "AN" (buoys) and "AX" (repeaters).

This raises some questions in my mind:

1. You say '"AB" or "AD" and maybe "AT" and "SA"'.  What are these different
talker prefixes supposed to mean?  I'd like to document them.

2. Where can I read about these and other NMEA 4.00 changes?

>                            My C skills are not that good, but 
> even I can copy-paste that code to support ABVDM/ABVDO.

I've done this, and added recognition of AN and AX too.

> I wonder if the right way to go is to treat **VDM and **VDO messages
> as AIS no matter the talker ID,

That wouldn't play well with the way the lexer is currently written.
It could be done, but I'd need a real user story before adding the
additional complexity.

> and I wonder if having the talker ID in the outputted 
> JSON would be of any practical use at this point.

Unclear.  I think we can actually deduce fixed/mobile pretty
reliably in other ways.
-- 
                <a href="http://www.catb.org/~esr/";>Eric S. Raymond</a>