[GRASS-user] Re: [GRASS-dev] r.out.gdal Gtiff output does not preserve color tables

[Dylan Beaudette]

On Thursday 28 February 2008, Patton, Eric wrote:
> >can you zoom a little bit so that the region is smaller than the raster
> >and then export with r.out.gdal to see whether it is still black?
> >Are you also getting warning about nulls in the data even if there
> >are none?
> >I think there is a bug in the program (and it also does not let you set
> >the number of decimal digits so it produces numbers with large number
> >of digits that are useless).
> >
> >thanks, Helena
>
> Helena,
>
> Zooming in to a smaller region than the raster doesn't change the results.
> I do get warnings about nulls, but it seems to make sense given the shape
> of the data I'm working with relative to the region.
>
> I exported a series of tiffs using r.out.gdal today, using type=Byte and
> type=UInt16. ArcGIS 9.2 was able to load the UInt16 tiffs, although very,
> very slowly. The elevation.10m raster from Spearfish took about 2 minutes
> to load, and it was only 5.6MB in size. The long loading time was due to
> the enormous size of the color table: 65,536 (2^16) colors. I can't imagine
> how long it would take Arc to load a 200MB tiff with this many colors. It
> would probably crash.
>
> All of the Byte tiffs were red. A look at the color table in Arc showed
> that all of the 255 colors were a repeating pattern of white-to-red (i.e.,
> 0-31, 32-63, etc.), with no green or blue colors.
>
> I've never had a problem with the output from r.out.tiff, using it for 6
> years now. I can view these tiffs in every image viewer and GIS on both
> Linux and Windows. I imagine the reason for this is the relatively
> simplified color tables in r.out.tiff tiffs? I would be great if there was
> a way to get georeferencing information installed in the headers of tiffs
> created from r.out.tiff. The output from r.out.gdal seems to be either way
> too detailed, or not mapped properly into a 255 color space.
>
> Has anyone had success using the type=Byte in r.out.gdal to get
> consistently good output for use in other GIS?
>

I ran into some of these problems a while back and posted [1] some thoughts on 
the matter. I updated the linked page today with an example using SVN GRASS 
and ArcMap 9.2.

In summary:

- r.out.gdal never worked for me (or rather the resulting file would not open 
in ArcMap)

- r.out.arc always worked, but file size problems can arise due to the ASCII 
nature of the output file. also the output file lacks spatial reference 
system data.


1. http://casoilresource.lawr.ucdavis.edu/drupal/node/337



-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341