[GRASS-user] Accessing a z-profile...

Jonathan Greenberg greenberg at ucdavis.edu
Fri May 30 19:06:42 EDT 2008

We're interested in working within GRASS to do some spectral analyses, 
but we need to be able to access a z-profile programatically, more or 
less on a pixel-by-pixel basis (e.g. we don't think we can use r.mapcalc 
to solve our problems).  Here's a for instance, and let me know if this 
is doable with existing commands and, if not, if there are standard 
GRASS "z-profile" access techniques:

For an image of B bands (in grass, I think this is represented as 
rastername.bandnumber), we want to calculate a weighted average of the 
bands which are, say, the 5 highest values in the stack.  Which 5 bands 
are the highest will change from pixel to pixel. 

On an array level, this is a sort function, but is there any algorithm 
already built into GRASS that can deal with pixel-level sorting (and use 
in mapcalc) and, if not, are there some good example code for access 
pixel-by-pixel an image and performing some sort of function on this stack.

I hope this was clear enough.  Thanks!


Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N
Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307

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