Sven Geggus wrote:
Hi there,
looks like ogr2ogr just ignores my nadgrids projection parameters :(
Here is what I have:
ogr2ogr -s_srs '+proj=tmerc +lat_0=0 +lon_0=12 +x_0=4500000 +y_0=0 \
+k=1.000000 +ellps=bessel +units=m +nadgrids=./BETA2007.gsb' \
-t_srs '+proj=longlat +datum=WGS84' -f "ESRI Shapefile" out.shp in.shp
ogr2ogr -s_srs epsg:31468 -t_srs epsg:4326 -f "ESRI Shapefile" out.shp in.shp
While the latter works fine. The first version does not seem to honor the
nadgrids Option. This is at least what strace hints me to. The command does
not even try to open the BETA2007.gsb file.
Testing the same Parameters wirth cs2cs does work as expected and
BETA2007.gsb _is_ honored:
echo 4450457 5487214 | cs2cs -f "%.12f" +proj=tmerc +lat_0=0 +lon_0=12 \
+x_0=4500000 +y_0=0 +k=1.000000 +ellps=bessel +units=m \
+nadgrids=./BETA2007.gsb +to +init=epsg:4326
Sven,
The thing to know about using PROJ.4 strings with GDAL/OGR is that GDAL/OGR
internally turns them into WKT. Anything in a PROJ.4 string that is not
preserved in the WKT is lost - and this includes nadgrids directives for
which there is no obvious WKT analog.
One workaround is to add +wktext to the PROJ.4 definition. This tells
GDAL to embed a complete copy of the PROJ.4 definition in the WKT as
an EXTENSION element so the original PROJ.4 string can be reconsistuted
exactly later.
Best regards,
--
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I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
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