On Wed, 2008-09-24 at 14:41 +0200, Markus Metz wrote: > > Nikos Alexandris wrote: > >> r.info composite_b123 -tr > >> > > min=0 > > max=32767 > > datatype=CELL > > [Raster MASK present] > > > > 1st attempt to export: > > > r.out.gdal in=composite_b123 > > out=/home/nik/grassdb/peloponnese/data/exports/composite_b123.tif > > Exporting to GDAL data type: UInt16 > > Segmentation fault > > [Raster MASK present] > > > > 2nd attempt to export without any change: > > > >> r.out.gdal in=composite_b123 > >> > > out=/home/nik/grassdb/peloponnese/data/exports/composite_b123.tif > > Exporting to GDAL data type: UInt16 > > Warning 1: Lost metadata writing to GeoTIFF ... too large to fit in tag. > > 100% > > WARNING: Input raster map constains cells with NULL-value (no-data). The > > value -32768 was used to represent no-data values in the input > > map.You can specify nodata value by nodata parameter. > > Warning 1: Lost metadata writing to GeoTIFF ... too large to fit in tag. > > r.out.gdal complete. > > [Raster MASK present] > > > > > Apart from the segmentation fault answered by Glynn, I see more problems > here. > > The nodata value of -32,768 is not valid, effectively discarding nodata > information, because the range of UInt16 is 0 to 65,535 and -32,768 is > out of range, i.e. there are no cells with -32,768 in the output > GeoTIFF. The range of composite_b123 is 0 to 32,767, therefore a > reasonable nodata value would be anything between 32,768 and 65,535. You > can try to use r.out.gdal with the options e.g. type=UInt16 nodata=32768 > or type=Int16 nodata=-32768. Generally it seems to be a good idea to > specify the options type and nodata (if needed) for r.out.gdal > > The next problem I suspect is the export of a raster probably generated > with r.composite (as the name suggests). This will only be displayed > with the same colours as in GRASS if the colortable provided with the > GeoTIFF metadata is properly interpreted. As I have shown previously [1] > this is not always the case, especially for UInt16, even GRASS struggles > with the re-import of UInt16 type GeoTIFFs [2]. A safer alternative > would be to put the three rasters used for r.composite in a group and > export the group with type=Byte if possible. The resulting GeoTIFF > should be a RGB image that can be displayed with any image viewer, an > easy way to check that the three bands are assigned red, green, and blue > as intended, otherwise swap the order in the ref file. > > I hope that helps > > Markus > > [1] http://trac.osgeo.org/grass/ticket/73#comment:13 > [2] http://trac.osgeo.org/grass/ticket/73#comment:15
Markus, your attention to details is very much appreciated. The above reported range is from a composite image created r.composite. But it was just a test to see whether it works or not. I can't export any viewable composite (at least for OpenEV with which I work) if max value exceeds 255. It works if you use levels=x (where x something which will give a max < 256 --- in my case it was levels=6). Anyhow, exporting the group of 3 bands with r.out.tiff or r.out.gdal works but there is something important: I don't like the white background. I would like to have a black backgroud surrounding my map. I could not get that really. I think I managed to see that only when I reduced levels with r.composite. Don't remember right now but I think rescaling initial bands with range from 0 up to 8000 in to 0 to 255 and export the group did not work either. If I am not wrong this has to do with transparency. I was trying all possible export methods (r.out.gdal, r.out.tiff, r.out.png) but I didn't nail a good method. Thank you, Nikos _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
