[aprssig] APRS LAT/LONG standards

[Curt Mills]

On Sat, 28 May 2005, Stephen H. Smith wrote:

> WGS84 is also the "official" datum of APRS for
> the same reason DD MM.mmmm format is -- it spews forth by default from GPS
> receivers.

By default, yes.  As soon as you change your displayed datum on a
Garmin receiver it will change the datum for the NMEA data stream
coming out the serial port as well.  Unfortunate, but the way it
works.

APRS was originally designed assuming that the GPS would always
output serial data in WGS84, and I think all or most of the GPS's at
the time worked that way.

You can try it yourself by hooking the GPS to a terminal program and
then changing the datum between NAD27 and WGS84.  Watch your
lat/long numbers change.

-- 
Curt, WE7U.				archer at eskimo dot com
http://www.eskimo.com/~archer
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