[PROJ] Determine if same celestial body, prior to 8.1

[Even Rouault]

Hi Nyall,

as the concept of celestial body doesn't exist in the ISO 19111 model 
used by PROJ, and by WKT, PROJ has a fuzzy identification logic to find 
to which known celestial body an ellipsoid belongs to by checking that 
the relative difference between their semi-major axis is <= 0.005. That 
value was found to work at least with all commonly used ellipsoids for 
Earth.

See 
https://github.com/OSGeo/PROJ/blob/c44a3008b0edb5197b0efa584d3f5f7e18d79b0b/src/iso19111/factory.cpp#L1809

Even

Le 25/05/2021 à 06:14, Nyall Dawson a écrit :
> Hi list,
>
> I'm wondering if there's any way in proj versions < 8.1 to determine
> (from the C api) whether two ellipsoid objects refer to the same
> celestial body?
>
> Ellipsoid::celestialBody() wasn't exposed to C api prior to 8.1, and
> that's the method used by proj internally in
> createOperationsGeodToGeod to determine whether two ellipsoids belong
> to the same body.
>
> Nyall
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