[FWTools] crs definition with both +nadgrids and +towgs84 parameters

"SAEZ Laurent - CETE Méditerr./DI/ETER" Laurent.Saez at developpement-durable.gouv.fr
Fri Jan 9 09:43:30 EST 2009

Thanks Frank for your quick response,

I ask this because IGN puts both parameters in its IGNF catalog.
I wonder if it is not preferable to specify only one.
My main problem is to be sure that the grid ntf_r93.gsb is used by  
MapServer for NTF to RGF93 transformations.

I'll do some tests.



Le 09.01.2009, "> Frank Warmerdam (par Internet)"  
<warmerdam at pobox.com> a écrit:

> SAEZ Laurent - CETE Méditerr./DI/ETER wrote:
>> Hi list,
>> Someone could tell me what appens if +nadgrids and +towgs84 are  
>> both  used in a crs
>> definition (e.g. in the EPSG file) ?
>> Which parameter is taken into account ?
>> Is the behavior the same in all tools (cs2cs, ogr utilities, gdal   
>> utilities, mapserver,PostGIS...) ?
> Laurent,
> I do not know which takes precidence ... the only answer I would trust would
> be one based on experimentation, so you might as well experiment.
> GDAL/OGR's parsing of PROJ.4 strings is likely to be different than their
> direct use in PROJ.4 itself.
> Best regards,
> -- 
> ---------------------------------------+--------------------------------------
> I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
> 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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