[gdal-dev] ogr2ogr using grid shift files

[Michael Schulz]

Hi Andre and Even,

thanks a lot for this clarification. Especially the last hint from Even
solved my issue, although widely using this syntax, I wasn't aware of the
subtle difference it makes.

Cheers and thanks, Michael

2018-03-07 23:13 GMT+01:00 Even Rouault <even.rouault at spatialys.com>:

> 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
>
>
>
>
>
> --
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>



-- 
-----------------------------------------------------------
Michael Schulz
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