[PROJ] Geodetic vs Geocentric

[Even Rouault]

Le 18/10/2023 à 17:57, Javier Jimenez Shaw via PROJ a écrit :
> Hi
>
> What is the difference between PJ_TYPE_GEODETIC_CRS and 
> PJ_TYPE_GEOCENTRIC_CRS?

Geocentric is a specialization of Geodetic (not in the standard, but so 
common that we have a subtype for it)


> In crs-explorer.proj.org <http://crs-explorer.proj.org> you can easily 
> see how there are no Geodetic systems in EPSG and there are no 
> Geocentric systems in IAU_2015...

Geodetic CRS in EPSG are geographic 2D, geographic 3D or geocentric. No 
weird/unusual geodetic ones


In IAU_2015, there's indeed no geocentric CRS definition. You may get 
PJ_TYPE_GEODETIC_CRS for CRS like IAU:19902 "Mercury (2015) / Ocentric" 
whose coordinate system is spherical with planetocentric latitude and 
longitude. This is close to a geographic CRS, except that you use 
-ocentric latitude (angle between the equatorial plane and the point on 
the ellipsoid) instead of a -ographic latitude (the angle between the 
equatorial plane and the normal to the ellipsoid at the point of interest).

-- 
http://www.spatialys.com
My software is free, but my time generally not.
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