[GRASS-dev] Re: [GRASS GIS] #73: r.out.gdal tiff output does not work

[GRASS GIS]

#73: r.out.gdal tiff output does not work
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  Reporter:  helena       |       Owner:  grass-dev at lists.osgeo.org
      Type:  defect       |      Status:  new                      
  Priority:  critical     |   Milestone:  6.4.0                    
 Component:  Raster       |     Version:  svn-trunk                
Resolution:               |    Keywords:  r.out.gdal, tiff         
  Platform:  Unspecified  |         Cpu:  Unspecified              
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Comment (by martinl):

 Replying to [comment:45 mmetz]:
 > r.out.gdal and r.out.tiff do two fundamentally different things and IMHO
 should be neither compared nor merged.
 >
 > r.out.tiff exports an image that can be viewed with any image viewer and
 looks like what you see on the grass display. The pixel values are most
 likely very different from the raster map that is exported, because with
 the -p flag everything is converted to Byte. Without the -p flag, the
 pixel values are the colour values of the color table, not the raster
 values. r.out.tiff output is thus not meant to be suitable for spatial
 analysis (like a screenshot of the display).
 >
 > r.out.gdal exports data, by default with a color table for data
 visualization if supported by the selected output format. The color table
 is just for convenience and not needed for analysis. Data export was
 successful if r.univar or some equivalent in another GIS software package
 gives results identical to r.univar on the grass raster. There is a
 difference between "can read the GeoTIFF" and "displays the GeoTIFF like
 grass displays the original raster", therefore the display is not suitable
 for testing because there are too many reasons why the display can be
 different (different monitor with different settings, different OS with
 different gamma, file format does not support color tables, conversion
 from color rules to color tables can introduce slight modifications, other
 GIS software uses different graphics engine, other GIS software can not
 read embedded color table).
 >
 > Sorry for being so thick, but I want to make the point of distinguishing
 images and data. Unfortunately, a .tif file can be both.

 thanks for the clarification. I didn't know that. Probably it should be
 explained more deeply in the manual page.

 Martin

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Ticket URL: <http://trac.osgeo.org/grass/ticket/73#comment:46>
GRASS GIS <http://grass.osgeo.org>