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.<br><br>Regards<br>
<br>Jose' A. Gonçalves<br><br><br><br><br><div class="gmail_quote">2011/4/29 Jan Hartmann <span dir="ltr"><<a href="mailto:j.l.h.hartmann@uva.nl">j.l.h.hartmann@uva.nl</a>></span><br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<br>
(About creating a grid shift file for the Dutch RD projection):<br>
<div class="im"><br>
On 04/08/11 18:29, Frank Warmerdam wrote:<br>
> As input we would require an input raster with two "bands"<br>
> representing the<br>
> offset in longitude and latitude. I'm not sure off hand what the units<br>
> are - possibly arcseconds? The input file would need to be<br>
> georeferenced<br>
> in latitude and longitude.<br>
><br>
> If your input points are sparse and irregular you could likely use<br>
> gdal_grid to interpolate a grid from the point data.<br>
><br>
> My point was mainly that you don't necessarily have to write an NTv2<br>
> "writer" - it is sufficient to get the datum shift data into any GDAL<br>
> support grid format.<br>
><br>
> Best regards,<br>
><br>
</div>I made a 400*400 gdal raster called dxy.tif with two bands, the first<br>
with offsets for longitude, the second for latitude, all in arcseconds.<br>
If I use this file in the +nadgrids clause of cs2cs, I don't see any<br>
difference in the output. If I change the filename into something<br>
non-existing, I don 't see any differences either and do not get an<br>
error message. Any idea how I can test this further?<br>
<br>
Jan<br>
<br>
Driver: GTiff/GeoTIFF<br>
Files: dxy.tif<br>
Size is 400, 400<br>
Coordinate System is:<br>
GEOGCS["RT38",<br>
DATUM["Stockholm_1938",<br>
SPHEROID["Bessel 1841",6377397.155,299.1528128000008,<br>
AUTHORITY["EPSG","7004"]],<br>
AUTHORITY["EPSG","6308"]],<br>
PRIMEM["Greenwich",0],<br>
UNIT["degree",0.0174532925199433],<br>
AUTHORITY["EPSG","4308"]]<br>
Origin = (3.386235000000000,50.762069400000001)<br>
Pixel Size = (0.009627452750000,0.007066402750000)<br>
Metadata:<br>
AREA_OR_POINT=Area<br>
Image Structure Metadata:<br>
INTERLEAVE=PIXEL<br>
Corner Coordinates:<br>
Upper Left ( 3.3862350, 50.7620694) ( 3d23'10.45"E, 50d45'43.45"N)<br>
Lower Left ( 3.3862350, 53.5886305) ( 3d23'10.45"E, 53d35'19.07"N)<br>
Upper Right ( 7.2372161, 50.7620694) ( 7d14'13.98"E, 50d45'43.45"N)<br>
Lower Right ( 7.2372161, 53.5886305) ( 7d14'13.98"E, 53d35'19.07"N)<br>
Center ( 5.3117256, 52.1753499) ( 5d18'42.21"E, 52d10'31.26"N)<br>
Band 1 Block=400x1 Type=Float64, ColorInterp=Gray<br>
Band 2 Block=400x1 Type=Float64, ColorInterp=Undefined<br>
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