[gdal-dev] Force application of ntv2 grid

[Andre Joost]

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