Hello<br><br>I have a program to create GSB files from two long/lat difference grids in Surfer format.<br><a href="http://www.fc.up.pt/pessoas/jagoncal/coordenadas/write_gsb.exe">http://www.fc.up.pt/pessoas/jagoncal/coordenadas/write_gsb.exe</a><br>
<br>You can check with it. The longitude difference in the input grid are in the standard way (east positive).<br><br><br>Regards<br><br>José A. Gonçalves<br><br><br><br><br><div class="gmail_quote">2013/1/17 Jan Hartmann <span dir="ltr"><<a href="mailto:j.l.h.hartmann@uva.nl" target="_blank">j.l.h.hartmann@uva.nl</a>></span><br>
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<font face="Times New Roman, Times, serif">(Sorry for crossposting,
don't know if it is a gdal or proj problem )<br>
<br>
This has been discussed on this list some time ago. I have been
able to create a working nadgrid file with gdal, but it doesn't
return the right coordinates. I did it as follows:<br>
<br>
- create a 4 band, float32 geotif, each pixel with the
displacements in lat, lon (arcseconds), errorx and errory (both
zero)<br>
- gdal-translate it to ntv2-format.<br>
<br>
The displacements in the geotiff are correct, and proj returns
shifted coordinates when using the ntv2-file, but not on the right
location. I'm really out of my wits. Could it have something to do
with ntv2 using negative lon-values east of Greenwich? Any help
would be appreciated.<span class="HOEnZb"><font color="#888888"><br>
<br>
Jan </font></span></font><br>
</div>
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