[Proj] Using Azimuthal Equidistant for Great/Small Circle Generation

Rob Iverson rob.iverson at gmail.com
Wed Mar 8 13:26:15 EST 2006

Sorry for the nearly-off-topic message here!  I don't know where else to

Is it valid to use the two-hemisphere form of the Azimuthal Equidistant
projection to compute great circles and small circles?

Here's what I have been doing:  I take a point that is the "center" of the
great/small circle, use that as the projection origin for azimuthal
equidistant, take the "radius" of the great/small circle (where 90 degrees
is a great circle), generate points on a circle centered at the middle of
the map, and inverse-project each of those points to get the coordinates on
the surface of the earth.

This certainly appears to give correct results, but I have no idea if it's
valid mathematically.

If it helps, I am currently using a spherical model of the earth, but I am
interested if this technique would work with the ellipsoidal models.

Thanks for your help!
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