[Gdal-dev] Recommendations for vertical data in GDAL

[Antoine Hue]

Le 3 mai 06, à 14:56, Frank Warmerdam a écrit :

>
>> b) doing any necessary mods to OGRCoordTransform to use such data 
>> when one or both of its spatialrefs are geocentric, and
>
> PROJ.4 already supports geocentric coordinate systems.  So I think we
> would just have to update the to/from PROJ.4 format translation code
> to support geocentric.
>
>> c) formalizing the list of avail. geocentric datums.
>
> Hmm, I'm not clear on what a geocentric datum is.

As far as I am concern, that is 3D modeling of terrains 
(www.petit-poucet.org), geocentric is very useful. Actually, I can 
either use projected or geocentric coordinates to represent a terrain 
in 3D. Geographic coordinates are useless. Projected are limited to 
small areas.

Our terrain modeling is based on the excellent Open Scene Graph 
osgTerrain library which is using GDAL for data access and warp. When 
the SRS is geographic, there is a further step to transform coordinates 
in geocentric using an approximate model of the ellipsoid.
When you say PROJ.4 supports geocentric coordinate systems, does it 
mean it could handle the geographic <-> geocentric conversions?


Antoine Hue