On Thu, Jan 28, 2010 at 2:01 AM, Smart, Gary <[email protected]> wrote: > We have tif maps which are OSGB grid aligned, but we need them aligned to > true-north. I presume this could be achieved by gdalwarp. Can anyone give > me a clue how to do this? Am I right in thinking that simply setting the > correct s_srs and t_srs would achieve everything I need? If so – what part > of the WKT would relate to Grid vs True?
Gary, It sounds like you want to reproject into a coordinate system that is aligned with the geographic lines of longitude. The most obvious candidate coordinate system is geographic coordinates themselves. If your existing grids are properly recognised as OSGB British National Grid, then it would be sufficient to do something like: gdalwarp -t_srs WGS84 in.tif out.tif If your input files do not have the coordinate system set properly, but *do* have georeferencing set in terms of british national grid meters, then you could force gdalwarp to understand the input coordinate system like this: gdalwarp -s_srs EPSG:27700 -t_srs WGS84 in.tif out.tif There are some other projected coordinate systems which are also aligned with the lines of longitude, including Mercator. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, [email protected] light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Programmer for Rent _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
