OSGeo
Support for triaxial ellipsoid projections
Hello, I was wondering if there are plans to implement support for triaxial ellipsoids. Although I see that the semiMedian_Axis is something that is included in the documentation for ellipsoids, from my understanding it is not something that is used anywhere. I want to be able to eventually plot projections with Cartopy using custom triaxial ellipsoids, which I know requires PROJ support. Thanks!
“Hi, I want to contribute to this feature. Can you guide me on small starter tasks such as updating documentation, adding warnings, or mapping out where ellipsoid parameters are used?”
Hi,
I am not sure if I can help you with these tasks... I can point you towards the math that might be relevant:
The wikipedia on this has links to relevant papers that have done the math you need to implement: https://en.wikipedia.org/wiki/Map_projection_of_the_triaxial_ellipsoid
This paper by Nyrtsov is particularly compelling. https://www.researchgate.net/publication/321983071_Conic_Projections_of_the_Triaxial_Ellipsoid_The_Projections_for_Regional_Mapping_of_Celestial_Bodies
Also this implementation for coordinate conversions on a triaxial ellipsoid was helpful to me: https://link.springer.com/article/10.1007/s00190-022-01650-9
Good luck!
@eitanrapa / @chikle9090: @cffk , the expert on the topic in our team , has recently communicated progress he's made on that topic in https://lists.osgeo.org/pipermail/proj/2025-October/011919.html and https://lists.osgeo.org/pipermail/proj/2025-November/011927.html . Such task would likely require quite solid math background.
