[gdal-dev] ogr2ogr using grid shift files

[Even Rouault]

On mercredi 7 mars 2018 17:45:41 CET Andre Joost wrote:
> Am 07.03.18 um 11:50 schrieb Michael Schulz:
> > Dear devs,
> > 
> > why is og2ogr using a grid shift file explicitely specified in the
> > proj4 string in the s_srs parameter and not when the same proj4 string is
> > in the system-wide proj4/epsg file?
> > 
> > This example gives correct projected results:
> > 
> > ogr2ogr -f 'ESRI Shapefile' target.shp -s_srs "+proj=tmerc +lat_0=0
> > +lon_0=9 +k=1 +x_0=3500000 +y_0=0 +ellps=bessel
> > +nadgrids=@BWTA2017.gsb,BETA2007.gsb +units=m +wktext" -t_srs "EPSG:25832"
> > source.shp
> > 
> > The proj4/epsg contains exactly the same definition for EPSG:31467, but
> > when used like this:
> > 
> > ogr2ogr -f 'ESRI Shapefile' target.shp -s_srs "EPSG:31467" -t_srs
> > "EPSG:25832" source.shp
> > 
> > the transformation is using the towgs84 parameters defined in
> > datum_shifts.csv...
> > 
> > Is this the intended behaviour?
> 
> Yes, this is intended. GDAL has its own CRS definition files, and does
> normally not fall back to the proj4 folder definitions.
> 
> C:\OSGeo4W64\share\gdal\datum_shift.csv is the file to look for,
> containg a definition for EPSG:4314 DHDN, which will be used for all
> DHDN based projected CRS.

Right, if you use "EPSG:XXXXX" as SRS name, GDAL will build the proj4 string from its various 
csv files in its data directory
If you want to use the definition from the proj.4 epsg file, use "+init=epsg:XXXXX" (on Unix, 
make sure to put 'epsg' in lowercase there, as this is the filename, so case sensitive)

Even


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