Question - raster statistics

[mike camann]

>I want to get some statistics that r.stats can't directly come up
>with, and I'm wondering if there is another function to do the trick.
>I have two raster maps: one has polygons defining different "landscape
>units".  The second is a crop yield "surface" from the same area.
>I want to know, for each landscape unit, not simply the total area,
>but also the mean yield, and standard deviation, etc.  So I need a
>routine that uses the landscape units map as a "mask", and calculates
>descriptive statistics from the raster values of the yield map found
>within the area of each polygon.

>Any suggestions?

>Tim.

> -----------------------------------------------------------------
>Tim Martin                     *
>Spatial Information Systems    *     If you want peace,
>University of Alberta          *     prepare for justice.
>martin at ulysses.sis.ualberta.ca *
>-----------------------------------------------------------------

Tim--

I don't know whether this will help you or not, but in the kind of
situation you discribe, I normally mask the raster file, then use
r.stats to either report cell counts (-c option) in each category or
list raw cell values to a file, then I process that file with another
analysis package-- S-plus in my case, but there are a number of others
available.  Writing a short program in the language of your choice to
read the file and perform summary statistics wouldn't be too difficult,
either.  No matter how you do it, you'll probably have to massage the
raw r.stats output before sucking it into the analysis package-- just
the kind of job sed and awk are good at.

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Michael Camann                          camann at dial.pick.uga.edu
Department of Entomology                camann at phoenix.cs.uga.edu
University of Georgia                   (706) 542-1388
Athens, GA 30602                        (706) 542-2276

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