# How to apply an affine transformation?

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## How to apply an affine transformation?

 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 TermensGeoprocess Department ICC _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj
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## Re: How to apply an affine transformation?

 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 <[hidden email]>: > 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 > [hidden email] > http://lists.maptools.org/mailman/listinfo/proj> _______________________________________________ Proj mailing list [hidden email] http://lists.maptools.org/mailman/listinfo/proj