[aprssig] APRS LAT/LONG standards

Stephen H. Smith wa8lmf2 at aol.com
Sat May 28 05:58:43 EDT 2005

aprs at pe1rdw.demon.nl wrote:

> Talking about gps standards, what datum are we using because in europe 
> wgs is default but I think the american continent has a different 
> datum as has  asia.
> 73 de Andre PE1RDW
WGS84 stands for WORLD Geodetic System of 1984,  and is the world-wide 
standard used by GPS (the GLOBAL positioning system).    A lot of older 
US maps are plotted to NAD27 (North American Datum of 1927) or NAD83 
(North American Datum of 1983).  NAD27 disagrees with WGS84 GPS readings 
by  hundreds of  feet in some parts of the US.   NAD83 agrees very 
closely with the GPS-derived WGS84  in North America. 

Most current North American electronic maps (Street Atlas, Microsoft 
MapPoint, Precision Mapping, etc) use WGS84 so that they can be used 
directly with the native mode of GPS for real-time moving map displays.  
Many of these mapping programs have now been brought into such close 
alignment with WGS84, that the real-time GPS display will clearly show 
not only whether you are on the east or west-bound side of a freeway but 
even whether you are in the fast or slow lanes (when you zoom them in to 
maximum magnification). 

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.

Stephen H. Smith             wa8lmf (at) aol.com
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