Add conversion from geodetic to geocentric spherical

[leouieda]

There is a function for converting latitudes from geodetic to geocentric but this is restricted to the surface of the ellipsoid. For many geophysical applications, we need to convert the (latitude, height) of points into (latitude_spherical, radius).

This is implemented in Boule as boule.Ellipsoid.spherical_to_geodetic. Boule is more focused on gravity calculations than coordinate conversions so I'd be happy to move that implementation to pymap3d if it's of interest to you.

I can volunteer to do this given a bit of guidance as to where to put the functions and what they should be called to fit with pymap3d.

[scivision]

We can make it a separate file under src/pymap3d/, and then import it from src/pymap3d/__init__.py like the others.
Maybe src/pymap3d/spherical.py ?
The function naming comes from Matlab/Octave, which I was replacing with Python when I made pymap3d years ago. Following that arbitrary naming scheme, perhaps spherical2geoetic() ?

[leouieda]

👍🏾 sounds good to me! I'll give this a shot and open a PR soon.

[ryanpavlick]

geodetic2geocentric already takes height above the sphreoid in to consideration: https://github.com/geospace-code/pymap3d/blob/1ecb84ecf3f81980b845dbfd94dbfdaa08339359/src/pymap3d/latitude.py#L86

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On Thu, Jun 16, 2022 at 6:40 AM Leonardo Uieda ***@***.***> wrote: 👍🏾 sounds good to me! I'll give this a shot and open a PR soon. — Reply to this email directly, view it on GitHub <#54 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABVI32FHDGBPT6J2EPEWKTVPMVC7ANCNFSM5Y3FE3NA> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[leouieda]

@ryanpavlick thanks for the pointer, I missed that when going over the latitude module. It takes into account but doesn't calculate the geocentric radius coordinate. From the docstrings it seemed like this was just for latitude so I didn't think to look further.

I already added the 2 functions to #55 but could change it to patch the existing geocentric2geodetic functions to return radius as well. But this would either break backwards compatibility or required another if flag then return block. I'm personally not fond of those since it the documentation becomes more confusing.