Support for more generic Space Oblique Mercator (SOM) projection

[sval-dev]

• Closes Support for more generic Space Oblique Mercator (SOM) projection #3337
• Tests added
• Added clear title that can be used to generate release notes
• Fully documented, including updating docs/source/*.rst for new API

[rouault]

To avoid the code duplication, if the only difference is hard-coded parameters vs user-provided one, a better way would be to have a common setup() method to misrom and genericsom, and have the entry points of the 2 functions call it. Like "utm" and "tmerc" in src/projections/tmerc.cpp (there are other similar instances in sconics.cpp, putp6.cpp, etc.)

[sval-dev]

I think I understand.

From my point of view, it looks like misrsom is a more specialized version of genericsom.

Would it work for you to keep the currently duplicated code in genericsom (with modification if necessary to support re-use) and modify misrsom to use the functions from genericsom rather than be duplicated?

[rouault]

Would it work for you to keep the currently duplicated code in genericsom (with modification if necessary to support re-use) and modify misrsom to use the functions from genericsom rather than be duplicated?

that's exactly what I meant :-) Basically you'd remove misrom.cpp entirely, and just move its entry point PJ *PROJECTION(misrsom) inside genericsom.cpp and make it reuse genericsom code but with the few needed parameters hardcoded.

[sval-dev]

Thanks! I'll make the change and push once more.