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Datums and Ellipsoids: NAD83, WGS84, and GRS80

Question asked by Vince Edwards on Sep 4, 2018

In my version of GPS Pathfinder Office (5.4), in the Software Help window under "About Coordinate Systems and Datums," I find the following text:


"Various datums have been established that best suit particular regions. For example, maps in the United States are often based on the North American Datum of 1927 or 1983 (NAD-27, NAD-83). The only global datum is WGS-84, which is based on the GRS-80 ellipsoid. All GNSS coordinates are based on the WGS-84 datum surface."


I find this to be a little confusing. My understanding is that the NAD-83 datum is based on (or "uses," whatever the proper word there would be) the GRS-80 ellipsoid, and the WGS-84 datum is based on its own ellipsoid of the same name (WGS-84). I know these two ellipsoids are remarkably close, however they are absolutely not the same thing. Is Pathfinder simplifying things by saying that the WGS-84 ellipsoid is based on the GRS-80 ellipsoid?


Thanks in advance if anyone can add some clarity.