[Proj] Dutch correction grid

[Jan Hartmann]

(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