Hi

I have Haversine great circle formula working to calculate distances

across a sphere for a GPS program.

Everyone knows the distance is virtually 2D on the Earth's surface,

and does not account for terrain.

Say I know there is terrain in a given area,

and the user is of higher elevation than where he/she started a track log,

I was thinking of using Pythagoras' theorem to attempt a better

overall distance estimation by taking horizontal land distance,

the difference between start and end elevation, and filling in the

3D distance with Pythagoras' theorem.

I don't mean for it to sound perfect, but should it not be a better approximation of overall distance every time?