[Proj] How to apply an affine transformation?

[Assumpcio Termens]

Thank you very much for your answer,

Generate a NTv2 grid was the first idea to apply, but I try to find if a
direct application would be possible and avoid datum shift files.

Thanks also for the information about the Spanish datum shift, I know it.
But in Catalonia -I'm working at the cartograhic agency for the local
government- we have our local datum transformation that it is more accurate
than Spanish one...

Best regards,

Assumpció.

2010/1/11 Jose Gonçalves <jagoncal at gmail.com>

> Hello
>
> I think there is no way of doing direct transformations between two
> cartographic coordinate systems (affine or other polynomial) with
> program CS2CS.
> Using command awk (unix/linux but also available for windows) you can
> do something like:
>
> awk '{print $1*A+$2*B+E,$1*C+$2*D+F}' < input_file.txt > output_file.txt
>
> where A,B,C,D,E and F are the parameters of your affine
> transformation. The input file must be a text file with Easting and
> Northing separated by space or tab, in the same way you would give to
> program CS2CS.
>
> If you really want to use CS2CS (or GDAL/OGR programs) you can create
> a datum shift grid file (GSB extension), with longitude and latitude
> differences, agreeing with the 2D direct affine transformation.
> There is the spanish grid file SPED2ETV2.gsb, which is available with
> the GVSIG software (and ArcGIS 9.3), which should do the conversion
> for all Spain with an accuracy of some 10 or 20 cm. Isn't it very
> close to your direct affine transformation?
>
> Regards
>
> José Gonçalves
>
>
> 2010/1/11 Assumpcio Termens <atermens at gmail.com>:
> > Hello to all,
> >
> > I'm a new user of PROJ library. I have to apply a transformation from
> > EPSG:23031 to EPSG:25831. The parametrization of the datum transformation
> is
> > an affine 2D transformation which has to be applied directly to UTM
> > coordinates. This parametrization is very useful in CAD environments, but
> I
> > don't know how to use in cs2cs or in GDAL/OGR library.
> >
> > Can I use this type of transformation in "cs2cs"?
> > Which options have to put in the comand line?
> > Or which files have to be modified?
> >
> > Thank you very much,
> >
> > Assumpció Termens
> > Geoprocess Department
> > ICC
> >
> >
> > _______________________________________________
> > Proj mailing list
> > Proj at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/proj
> >
>
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