[Gdal-dev] Warping of large files

[Asger Petersen]

Hi list

I would really appreciate some advice on this problem:
I have received a couple of large (½-1GB) ecw-files that are geocoded in an obscure coordinate system. I have to display these files via WMS using mapserver, so it is necessary to reproject them. I have a coordinate transformation program that allows me to transform the obscure coordinates to coordinates in more known systems like utm.

I imagined doing something like:
1) use gdal_translate to add GCPs with coordinates in utm
2) use gdalwarp to warp the image into utm projection
3) compress image to ecw (as our mapserver doesn't support jp2 at the moment)
This method is fine for small images, but it is not suitable for my large files because I can't get an appropriate rw+ format to work with the warp. Gtiff is out of the question as the resulting files are way too big for this format. Using the --formats option the JP2ECW is shown to be rw+, but the driver keeps throwing a "ERROR 5: destination band 1 appears to be read-only." error. As I understand it compressing large files to ecw could also be a problem due to some limitation in the ecw sdk.

Of course i could chop the files into pieces small enough to use Gtiff and then mosaik them in Mapserver, but I would really prefer keeping them in one piece.

Any advice on how to handle this are highly appreciated.

Regards
Asger Petersen