[gdal-dev] Datum shiftings

[Andre Joost]

Am 13.05.2013 12:34, schrieb Juan Pedro Pérez Alcántara:

>
> However, I'm still wondering... is GDAL using the local PROJ4 installation?
> Or does datum shiftings by itself? If so, why not to rely on PROJ4?

GDAL brings its own database, which is in sync with PROJ4. At least on 
Windows it will not look at other installations of PROJ.

Other Software handle projections and datum shifts seperately. For 
PROJ/GDAL it was decided to bundle them together in EPSG-Codes, which 
may lead to false results if users of other software reprojected with 
other parametres. And you should consider that datum shifts may be 
altered from one GDAL/PROJ version to the next, because local 
authorities may have published better shift parametres.

>
> And using the grid is something we always want to do. Is there any place in
> the GDAL config files where we can make the use of the grid permanent for a
> datum shift case in particular?

Only the North American grids are hardcoded in PROJ:

http://trac.osgeo.org/proj/browser/trunk/proj/src/pj_datums.c

And GDAL ist using them as well. You are free to add your datum, and 
compile from source for yourself.

Greetings,
André Joost