[Proj] Creating a nadgrid shift file

[Jan Hartmann]

Hi Jose, I can produce a working gsb file, but somehow the coordinate 
range is wrong. It must have something to do with the way the base grids 
are produced with gdal-grid. Could you give me an example of working 
long/lat distance grids (surfer is OK), and the way you made them?

Jan

On 01/18/2013 11:51 AM, Jose Gonçalves wrote:
> Hello
>
> I have a program to create GSB files from two long/lat difference 
> grids in Surfer format.
> http://www.fc.up.pt/pessoas/jagoncal/coordenadas/write_gsb.exe
>
> You can check with it. The longitude difference in the input grid are 
> in the standard way (east positive).
>
>
> Regards
>
> José A. Gonçalves
>
>
>
>
> 2013/1/17 Jan Hartmann <j.l.h.hartmann at uva.nl 
> <mailto:j.l.h.hartmann at uva.nl>>
>
>     (Sorry for crossposting, don't know if it is a gdal or proj problem )
>
>     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:
>
>     - create a 4 band, float32 geotif, each pixel with the
>     displacements in lat, lon (arcseconds), errorx and errory (both zero)
>     - gdal-translate it to ntv2-format.
>
>     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.
>
>     Jan
>
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