Landing locations on ellipsoidal bodies

[Askaniy]

Problem:
For bodies using constructions SemiAxes and Oblateness, the positions of locations are approximated by a sphere, and they are floating in space (see the screenshots below).

Way to solve:
Let's notice, that

• Celestia uses planetocentric (projection from center) coordinate system for texturing models and for their locations
• Celestia uses planetographic (projection by normal) for texturing ellipsoids, and spherical approximation for their locations

So, request is to implement recalculation of input planetographic longitude (λ), latitude (φ) and height (h) into x, y, z coordinates using ellipsoid proprieties (semiaxes a_x, a_y, b). I found the formulas in DOI 10.1007/s00190-011-0514-7:

(Duplicate here from the Discord server)

[375gnu]

@Askaniy could you provide test addons?

[Askaniy]

These locations of Ceres already in the content, I think they are good for testing

[375gnu]

The formulae should be adjusted a bit to match Celestia coordinate system but the result is good:

[375gnu]

But with an object placed on a planet surface image is broken due to #542:

So I gonna fix this for locations only for now.

[SevenSpheres]

At least with the build from the pull request, locations on Ceres are fixed with its actual oblateness, but I just found that if I modify an object to increase its oblateness to 0.5, locations are still floating in space: