[Proj] Creating a nadgrid shift file

Jose Gonçalves jagoncal at gmail.com
Fri Jan 18 05:51:14 EST 2013


I have a program to create GSB files from two long/lat difference grids in
Surfer format.

You can check with it. The longitude difference in the input grid are in
the standard way (east positive).


José A. Gonçalves

2013/1/17 Jan Hartmann <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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