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

[Frank Warmerdam]

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? 

Andreas,

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,
-- 
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