Or even simpler, compute geodesic distance on ellipsoid (a + h_mean, b +
h_mean) where h_mean is the mean of h_start and h_end. If h_start and
h_end are small compared to a, I would expect whatever mean formula used
to lead to similar results. At least this method is guaranteed to give
the correct result when h_start = h_end = 0 ...
Le 28/08/2024 à 01:36, Even Rouault via PROJ a écrit :
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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