[gdal-dev] GRASS export GeoTiff adventure :-)

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Sat Aug 2 08:37:52 EDT 2008

Many questions... Thank you in advance, Nikos :-)

Importing RGB tiff's (size: 2500, 2500 --- with INTERLEAVE=PIXEL) in
GRASS' database splits them, as expected, in red, green and blue raster
maps. After MASKing out unwanted areas, how should one export the maps
to end-up with tiff files similar (or improved) to the original ones?

1. Using r.composite and exporting with r.out.gdal gives "white" as
nodata. Whenever I set "nodata=0" I don't get a viewable photo

2. r.out.tiff does not provide a "nodata" option. What's the necessity
of r.out.tiff if r.out.gdal can do the same with more options?

3. GeoTiff metadata are lost always (?) while exporting with

4. The createopt="INTERLEAVE=PIXEL" is not respected by r.out.gdal (?)

r.out.gdal in=koblenz_2618_5566.red_i type=Byte
out=/home/nik/grassdb/rlp_fgaps/data/orthophotos/koblenz/test/koblenz_2618_5566.red_i2 createopt="INTERLEAVE=PIXEL,TFW=YES"

gdalinfo koblenz_2618_5566.red_i2

5. What is the correct way to import an rgb photo, process, export back
in GeoTiff?

6. Is it better to export the red, green and blue GRASS raster maps
one-by-one and merge them with gdal_translate (or gdal_merge.py)?

7. Exporting a group (the ones that automatically are created for each
imported photo and contain the red, green and blue components
respectively), gives "INTERLEAVE=PIXEL" but "Block=2500x3". Is it
correct to force createopt="BLOCKYSIZE=1" which gives "Block=2500x1"? 

8. I read in Markus' blog [1] how to "write out a GRASS raster map to
GeoTIFF -- this format 
includes the coordinates within the file's metadata" using
Doesn't r.out.gdal do that and if not why?

There is also that tiles provide "Fast image display...". From my small
experience, I can't really judge if TILES accelerate image display.
Sometimes I have the impression that they are slower that STRIPPED

8. There are several compression methods? Does compression affect
significantly reading/displaying an image?

9. Should one prefer another file format?


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