[aprssig] Re: GPS with compass
kc2mmi at verizon.net
Wed Mar 30 12:33:06 CST 2005
The Garmin GPS 76 does not contain a compass. Very few units actually do.
The compass "screen" on most GPSes (I'd say 99% of them) is just a rendering
based on the course and bearing information the GPS computes from the
satellites and cannot be trusted unless you are in fact moving.
The NMEA sentances provide for course, bearing, cross track error, and
other directional information. It all depends on which NMEA sentences you
are sending out, and which ones the receiver is capable of parsing. NMEA
provides for real compass information from a dedicated compass unit as well.
I don't know if the GPS "lies" and uses that data field, or sends
separately, but since marine integrators can take both instruments without
confusion, I suspect the 'real' compass strongs are different. You might
want to look up the NMEA specs on line to be certain.
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