aerial photo mosaic

[Simon Cox]

Joe - r.patch messes with the color table in an 
attempt to maintain the appearance of the output.  
It treats the raster's as category maps, rather than 
continuous fields, so pixels with similar values do 
*not* get assigned similar colors.  
However, since the GRASS display colour-space is 
restricted to 216 colours, this usually fails for 
rasters with a large number of categories, such as images.  

Images are a particular problem, of course, since adjacent 
scenes frequently have different average levels, so features 
which any intelligent observer would interpret as continuous 
across the join will be really messed up.  Mosaicing 
remote-sending images successfully is a long-standing 
problem.  If you intend to do quantitative analysis you 
more-or-less have to do it one frame at a time.  

If you just want somthing that looks OK, than try manipulating 
the color look-up-table, either manually by editing 

gisdbase/location_name/mapset/cell/colr/map 

or by using r.colors 
(NB d.colors only changes the display so 
does not persist between sessions).  


-- 
__________________________________________________
Dr Simon Cox - Australian Geodynamics Cooperative Research Centre
CSIRO Exploration & Mining, PO Box 437, Nedlands, WA 6009 Australia
T:  +61 8 9389 8421   F:  +61 8 9389 1906   Simon.Cox at dem.csiro.au
http://www.ned.dem.csiro.au/SimonCox