2013/12/10 stevejking <[email protected]> > Andre Joost wrote > > Am 29.11.2013 09:59, schrieb Jeremy Palmer: > >> Hi gdal-devs, > >> > >> I'm trying to shift shapefile data using a custom NTv2 grid file. The > >> logical source and destination coordinate systems are the same > >> (geographic coordinates EPSG:4167), I only want to shift the data. > >> > >> The type of command I'm trying to run is: > >> > >> ogr2ogr -f "Esri Shapefile" -a_srs "+proj=longlat +ellps=GRS80" > >> -t_srs "+proj=longlat +ellps=GRS80 +nadgrids=custom_grid.gsb +wktext" > >> dst_datasource_name src_datasource_name > >> > >> but the output shapefile does not get transformed... > >> > >> Is this because there is a short circuit in proj4 if the ellipsoids > >> are the same? > >> > > > > No, you have to explicitely specify +towgs84=0,0,0,0,0,0,0 for the first > > srs. Otherwise it is assumed that both share the same datum. > > > > HTH, > > André Joost > > > > _______________________________________________ > > gdal-dev mailing list > > > [email protected] > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev > > Andre is on the right track. > > But, I believe you need to specify the +nadgrids=c:\custom_grid.gsb in your > source projection, then use the +towgs84=0,0,0,0,0,0,0 in your target. > > You may get away without specifying any path to your gsb, not sure. > > > HTH > Regards, > Steve > > Hi,
Just as a side note, I like to turn on the debugging mode by setting the environment variable PROJ_DEBUG to any number. It gives useful info on how your ntv2 grid is used and might help you identify other issues if any. Regards Thomas -- Thomas Campagne Vancouver, BC Canada
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