[PROJ] Ellipsoidal distances, with different heights

[Nyall Dawson]

Hi list,

Let's say I have two points on an ellipsoid, with each point having a
different height above the ellipsoid. I want to calculate a kind of
"geodesic" between these points, where there's an assumption that the
gradient of the height-above-ellipsoid for the "geodesic" is constant.

Is this mathematically solvable? Or, more to the point, is it possible
to calculate this using any of the methods exposed via geodesic.h?

Nyall