[Qgis-developer] Difference for transform reference system between QGIS and GDAL

Andre Joost andre+joost at nurfuerspam.de
Fri Jan 17 07:19:30 PST 2014

Am 17.01.2014 11:56, schrieb Luiz Motta:

> The question is exact this, why the QGIS read the PRJ and understands the
> 'towgs84', otherwise, the GDAL don't understands, where , the QGIS use the
> GDAL/OGR provider ?

This is an intended behaviour.

Other software (like ESRI) don't write datum shifts in the .prj file, 
but leave it to the end user to select one of the available shifts. QGIS 
has to handle these files correctly, so it looks up the EPSG table and 
selects the best fitting code. If you think it has guessed wrong, you 
can assign another CRS to the layer.

GDAL does no guessing. Unless there are not datum shifts provided on 
source and target CRS (using either +datum, +towgs84 or +nadgrids), it 
does no datum shift at all. You can specify -s_srs to override the 
source file's .prj file with an EPSG code that contains a datum shift. 
This should bring the same result as QGIS does automatically.

André Joost

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