Hi Markus:
Thanks for the quick reply. That indeed was my problem:
misunderstanding the implications of the levels param.
Best,
Micha
On 29-Jan-15 12:28 PM, Markus Metz
wrote:
On Wed, Jan 28, 2015 at 10:34 PM, Micha Silver <[email protected]> wrote:
When I use r.composite to create, i.e., a false_color composite from three
Landsat bands, the RGB values in the composite are slightly different than
the values in the original bands. Why is that?
Because the number of levels to be used for each component is by
default 32, not 256 [0].
Markus M
[0] http://grass.osgeo.org/grass70/manuals/r.composite.html
Here's an example:
# Import three bands
GRASS 7.0.0svn (UTM33N):~/Downloads > for b in 2 3 4; do r.in.gdal --o
input=LE71830542003069SGS00_B${b}.TIF output=b${b}; done
r.in.gdal complete.
# Create composite
GRASS 7.0.0svn (UTM33N):~/Downloads > r.composite r=b4 g=b3 b=b2
out=false_color --o
Creating color table for output raster map...
100%
Writing raster map <false_color>...
100%
r.composite complete. Raster map <false_color> created.
GRASS 7.0.0svn (UTM33N):~/Downloads > r.info -g false_color
north=1065915
south=856485
east=731415
west=497985
# Choose a point for testing
GRASS 7.0.0svn (UTM33N):~/Downloads > x=600000; y=900000
# and query with r.what
GRASS 7.0.0svn (UTM33N):~/Downloads > r.what -n map=b4,b3,b2 coord=${x},${y}
easting|northing|site_name|b4|b3|b2
600000|900000||67|108|96 <<=============
GRASS 7.0.0svn (UTM33N):~/Downloads > r.what -n -r map=false_color
coord=${x},${y}
easting|northing|site_name|false_color|false_color_color
600000|900000||12712|065:106:098 <<============
GRASS 7.0.0svn (UTM33N):~/Downloads >
Thanks,
Micha
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