Thank you very much for your answer, <br><br>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. <br><br>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...<br>
<br>Best regards,<br><br>Assumpció.<br><br><div class="gmail_quote">2010/1/11 Jose Gonçalves <span dir="ltr"><<a href="mailto:jagoncal@gmail.com">jagoncal@gmail.com</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hello<br>
<br>
I think there is no way of doing direct transformations between two<br>
cartographic coordinate systems (affine or other polynomial) with<br>
program CS2CS.<br>
Using command awk (unix/linux but also available for windows) you can<br>
do something like:<br>
<br>
awk '{print $1*A+$2*B+E,$1*C+$2*D+F}' < input_file.txt > output_file.txt<br>
<br>
where A,B,C,D,E and F are the parameters of your affine<br>
transformation. The input file must be a text file with Easting and<br>
Northing separated by space or tab, in the same way you would give to<br>
program CS2CS.<br>
<br>
If you really want to use CS2CS (or GDAL/OGR programs) you can create<br>
a datum shift grid file (GSB extension), with longitude and latitude<br>
differences, agreeing with the 2D direct affine transformation.<br>
There is the spanish grid file SPED2ETV2.gsb, which is available with<br>
the GVSIG software (and ArcGIS 9.3), which should do the conversion<br>
for all Spain with an accuracy of some 10 or 20 cm. Isn't it very<br>
close to your direct affine transformation?<br>
<br>
Regards<br>
<br>
José Gonçalves<br>
<br>
<br>
2010/1/11 Assumpcio Termens <<a href="mailto:atermens@gmail.com">atermens@gmail.com</a>>:<br>
<div><div></div><div class="h5">> Hello to all,<br>
><br>
> I'm a new user of PROJ library. I have to apply a transformation from<br>
> EPSG:23031 to EPSG:25831. The parametrization of the datum transformation is<br>
> an affine 2D transformation which has to be applied directly to UTM<br>
> coordinates. This parametrization is very useful in CAD environments, but I<br>
> don't know how to use in cs2cs or in GDAL/OGR library.<br>
><br>
> Can I use this type of transformation in "cs2cs"?<br>
> Which options have to put in the comand line?<br>
> Or which files have to be modified?<br>
><br>
> Thank you very much,<br>
><br>
> Assumpció Termens<br>
> Geoprocess Department<br>
> ICC<br>
><br>
><br>
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</blockquote></div><br>