[gdal-dev] reprojection from BNG to WGS84 -- using gdalwarp

Frank Warmerdam warmerdam at pobox.com
Mon Mar 22 13:14:09 EDT 2010

Andreas Joisten wrote:
> Hi all,
> I have problem to reproject a raster file in BNG British National Grid to WGS84.
> gdalwarp -s_srs EPSG:27700 -tps -t_srs EPSG:4326 -co TFW=YES -r near input.tif geo_output.tif
> I have some questions:
> Must be the input file a GeoTiff file? 


No, gdalwarp will accept any GDAL supported raster format as input
as long as it has georeferencing.

> Which requirements must be met by the input file?

It must be georeferenced in some fashion.

> If the input file is a GeoTiff, do I need ground controlpoints?

By default gdalwarp will look for an affine transform, but I
see you have selected -tps which requires control points as input.
So yes, with -tps the input file would need to have 3 or more ground
control points.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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