How do I know what projection to use for north-up or 0 rotation? I have a gtiff (ND83-nf) that gives me the error when importing to Grass. Should I re-project or recreate the image with the rotation burned into the image? If I re-project what projection should I use? when I re-project in fwtools the default comes up as the same as the input. not sure what to choose. Thanks
I suppose you got the error "ERROR: Input map is rotated - cannot import." with r.in.gdal.
In this case the image must be first externally rotated, applying the rotation info stored in the metadata field of the raster image file. For example, the gdalwarp software can be used to transform the map to North-up (note, there are several gdalwarp parameters to select the resampling algorithm):
gdalwarp rotated.tif northup.tif
You will not be rotating your image, you will just be resampling it to a grid (raster) that is north-up. The output raster of gdalwarp is automatically resampled to a north-up raster with the projection that you have chosen with the option -t_srs.