sensitivity analysis

[mike camann]

grassu-list'ers

Here is an interesting problem that I would appreciate some input on
before I re-invent the wheel, so to speak.  I need to do a sensitivity
analysis on a spatial model to test its robustness to
mis-classifications in the underlying data layers.  To do this, I need
to randomly select a fixed percentage of polygons within each map
layer, and reclassify them to random categories within the set of
possible categories for that map.

For example, suppose a layer called forest.soils has 50 categories in
400 polygons, and I want to reclassify 5 percent of them.  I would then
need to randomly select 20 polygons from the set of 400, and reclassify
each to a random value between 1 and 50 (I'm excluding NO_DATA from the
present analysis).  This new, perturbed map layer would then be used as
input to the spatial model.

Any thoughts on the best way to proceed?  Is there a pre-existing GRASS
facility for doing random reclassifications (I suspect not...)?  How
might I string together other GRASS tools to do this?

Any help would be appreciated.

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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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