[Xastir] GNGGA vs GPGGA support

[Jason KG4WSV]

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