[Proj] Dutch correction grid

[Jose Gonçalves]

The +nadgrid command expects a NTv2 file, with extension gsb, not a tiff
file. You must use gdal_translate to convert it to the NTv2 format. I think
that's what Frank Warmerdam referred in a previous email.

Regards

Jose' A. Gonçalves




2011/4/29 Jan Hartmann <j.l.h.hartmann at uva.nl>

>
> (About creating a grid shift file for the Dutch RD projection):
>
> On 04/08/11 18:29, Frank Warmerdam wrote:
> > As input we would require an input raster with two "bands"
> > representing the
> > offset in longitude and latitude.   I'm not sure off hand what the units
> > are - possibly arcseconds?   The input file would need to be
> > georeferenced
> > in latitude and longitude.
> >
> > If your input points are sparse and irregular you could likely use
> > gdal_grid to interpolate a grid from the point data.
> >
> > My point was mainly that you don't necessarily have to write an NTv2
> > "writer" - it is sufficient to get the datum shift data into any GDAL
> > support grid format.
> >
> > Best regards,
> >
> I made a 400*400 gdal raster called dxy.tif with two bands, the first
> with offsets for longitude, the second for latitude, all in arcseconds.
> If I use this file in the +nadgrids clause of cs2cs, I don't see any
> difference in the output. If I change the filename into something
> non-existing, I don 't see any differences either and do not get an
> error message. Any idea how I can test this further?
>
> Jan
>
> Driver: GTiff/GeoTIFF
> Files: dxy.tif
> Size is 400, 400
> Coordinate System is:
> GEOGCS["RT38",
>     DATUM["Stockholm_1938",
>         SPHEROID["Bessel 1841",6377397.155,299.1528128000008,
>             AUTHORITY["EPSG","7004"]],
>         AUTHORITY["EPSG","6308"]],
>     PRIMEM["Greenwich",0],
>     UNIT["degree",0.0174532925199433],
>     AUTHORITY["EPSG","4308"]]
> Origin = (3.386235000000000,50.762069400000001)
> Pixel Size = (0.009627452750000,0.007066402750000)
> Metadata:
>   AREA_OR_POINT=Area
> Image Structure Metadata:
>   INTERLEAVE=PIXEL
> Corner Coordinates:
> Upper Left  (   3.3862350,  50.7620694) (  3d23'10.45"E, 50d45'43.45"N)
> Lower Left  (   3.3862350,  53.5886305) (  3d23'10.45"E, 53d35'19.07"N)
> Upper Right (   7.2372161,  50.7620694) (  7d14'13.98"E, 50d45'43.45"N)
> Lower Right (   7.2372161,  53.5886305) (  7d14'13.98"E, 53d35'19.07"N)
> Center      (   5.3117256,  52.1753499) (  5d18'42.21"E, 52d10'31.26"N)
> Band 1 Block=400x1 Type=Float64, ColorInterp=Gray
> Band 2 Block=400x1 Type=Float64, ColorInterp=Undefined
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