[Xastir] GNGGA vs GPGGA support

[Tom Russo]

Turns out that the GNGGA/GNRMC vs. GPGGA/GNGGA issue is the reason for
the newly opened issue #53 on github (https://github.com/Xastir/Xastir/issues/53), 
and I believe I have it fixed with pull request #58 (https://github.com/Xastir/Xastir/pull/58)

If any users with GLONASS receivers that emit GNGGA/GNRMC sentences (such
as the DRAWS hat for Raspberry Pi) would like to test it out, 
you can get it via:

   cd <your clone>
   git checkout master
   git checkout -b tvrusso-feature-supportglonass master
   git pull https://github.com/tvrusso/Xastir.git feature-supportglonass

Then rebuild Xastir and try it out.

The more folks I can get testing this the better.  I won't merge to master
until I at least confirm that it helps the GN vs. GP thing.  As far as I can
tell so far, I haven't borken it for GP.

On Sun, Dec 02, 2018 at 02:52:06PM -0600, we recorded a bogon-computron collision of the <kg4wsv at gmail.com> flavor, containing:
> I just started playing with a u-blox 8 family GPS.  It's capable of
> receiving multiple GNSS simultaneously. At first glance this unit doubles
> the number of available satellites just because it's listening to GLONASS
> and GPS at the same time.
> 
> Of course there's a downside. In APRS-land we're used to dealing with a
> single "talker ID" that indicates we're dealing with GPS (the name of the
> US system) - that's the "GP" in GPGGA and GPRMC. This system uses GN as the
> talker ID when it's listening to multiple systems.  I can configure it to
> use GPS only and get my familiar GPGGA, but I stop listening to a bunch of
> available satellites when I do that.
> 
> Since APRS has limited resolution we (APRS users) wouldn't benefit much
> from increased accuracy, but we would get something from having a much
> larger constellation available.
> 
> Has anyone messed with these multi-GNSS receivers? Are the benefits that
> seem obvious at first glance real?
> 
> Would it be appropriate to think about code changes to Xastir (or other
> clients but i don't use those) to use G[PLABN]GGA or G[PLABN]RMC instead of
> restricting ourselves to GP only? There would be 2 cases here, once for the
> attached GPS interface to determine our position, and the GPGGA APRS packet
> type.  I'm actually considering using GGA and RMC packets to get increased
> resolution on a non-144.39 tracking application.
> 
> Does xastir verify the NMEA checksum from an attached GPS?
> 
> -Jason
> kg4wsv
> _______________________________________________
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> Xastir at lists.xastir.org
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-- 
Tom Russo    KM5VY
Tijeras, NM  

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