[PROJ] Ellipsoidal distances, with different heights

[Even Rouault]

Nyall,

I'm not sure there's a real definition to what you want to accomplish.

I guess I would :

- use the geod_position() of geodesic.h to compute a sufficient number 
of intermediate positions

- linearly interpolate the ellipsoidal height

- convert the resulting (lon, lat, h) to geocentric (X, Y, Z) using 
+proj=cart

- use 3D Cartesian distance to compute each intermediate segment

- sum them up

A cheaper alternative might be to compute the geodesic distance between 
the start and end points both on the ellipsoid (a + h_start, b + 
h_start) and on the one (a + h_end, b + h_end), and compute some sort of 
mean (arithmetic, geometry, ... ?) on those 2 distances.

Even


Le 28/08/2024 à 01:06, Nyall Dawson via PROJ a écrit :
> 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
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