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ellipsoidal distance

The shortest distance between two points on earth taking into account the actual shape of the earth, as opposed to conventional great circle distance, which assumes a spherical earth.

This is the distance that GPS units use when they compute distance between points. They first read the datum (shape of the earth) selected in the GPS unit, and then use that model to compute the distances, which are then ellipsoidal distances.

You can compare, say, WGS84 to a spherical earth at this Ed Williams link. In principle, this computation will give different results for different choices of end points, even though the spherical earth distances would be the same. Note, too, that he calls the distance "great circle" regardless of the ellipsoid in use. It seems tidier to use different names, however, since we do have different computations and different results.


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