[GRASS-user] GRASS export GeoTiff adventure :-)

Markus Metz markus_metz at gmx.de
Sat Aug 2 16:47:23 EDT 2008

I think exporting colour tables is one big problem [also see 3, 4]: 
GeoTIFFs exported from GRASS suddenly became readable after deleting the 
colour table before exporting (my own fiddling around). IMHO, there 
should be an option to export colour tables with default to no. There 
should also be a warning if you really want to export a colour table. 
For multiband images (exporting a group), exporting colour tables might 
need to be disabled completely. This is easy to implement in the current 
version of r.out.gdal. In my experience, Tiffs without a colour table 
are indeed useful [contrary to 4], because for imagery, most viewers 
have their own contrast enhancement and colour table manipulation 
methods. For a raster with labelled categories, a separate text 
file/table with labels and maybe a suggested colouring scheme needs to 
be provided anyway. I haven't found yet a raster format that gdal can 
write where gdal can export category labels from GRASS.

Another issue might be handling of nodata, that is at least a starting 
point for testing/fixing.

There might be other problems with the readability of the output of 
r.out.gdal, but maybe sorting out the two problems listed above helps a lot.

Having said that, r.out.gdal and GDAL Utility Programs as they are now 
are probably unmatched in their compatibility and interoperability [5].



Dylan Beaudette wrote:
> I am glad that this topic is getting some traction again. I have
> noticed that r.out.gdal does not always produce images readable in
> ESRI products. Heck, sometime the resulting TIFF would not even be
> readable by QGIS. This was some time ago, and associated with several
> blog postings / trac tickets:
> Posts:
> 1. http://casoilresource.lawr.ucdavis.edu/drupal/node/337
> 2. http://gfoss.blogspot.com/2008/06/gdal-raster-data-tips-and-tricks.html
> Ticket:
> 3. http://trac.osgeo.org/grass/ticket/73
Other posts:
4. http://lists.osgeo.org/pipermail/grass-dev/2008-February/035987.html
5. http://lists.osgeo.org/pipermail/grass-user/2008-July/045860.html
> It would be a good idea to get this fixed in GRASS64 before marching
> into GRASS7 as import/export operations are fundamental to GIS work.
> Cheers,
> Dylan

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