[gdal-dev] CoordinateTransformation towgs84 parameter

[Frank Warmerdam]

Mendizabal Vicente, Ainhoa wrote:
> Hi all,
> 
>  
> 
> I just want to know if the “OGRCreateCoordinateTransformation” function 
> takes into account the names of the datums involved (specified in the 
> WKT), or if it is necessary to specify the TOWGS84 parameter for each 
> Coordinate System. In this case, where I can get this parameter for each 
> datum?

Ainhoa,

The names of datums are generally not significant to OGR, with a few
exceptions (ie. special rules for recognising NAD27 for instance).

Generally, with the exception of NAD27, you should attempt to provide a
TOWGS84 parameter if you want datum shifts.

Finding appropriate values is difficult.  The EPSG database has some (often
multiple possibilities per datum).  There are a variety of other sources,
such as national mapping agencies.  Which value is best often depends on
the region of interest within the applicable area of the datum.

I have no good answer.

Best regards,
-- 
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