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[chuck at pollux.GEOG.UCSB.EDU]

>Reply-To: grassu-list at max.cecer.army.mil
>Subject: reducing grid size of elevation data

>Although I know it's not accurate to resample 30 m grid size elevation
>data to 10 m grid size, I want to do this to improve my display since
>other layers are 10 m grid size.

>What is a good method for doing this?  r.surf.idw etc. seem to assume
>random points.  I would like the center of each 9 cells that used to be
>one cell to remain the same, and the outer 8 to become an averaged value
>of their neighbors.  I am thinking of using r.neighbors.  Has anyone
>done anything like this?  I promise I will not claim that it is accurate
>10 m elevation data -- it will just look a little better.

>Thanks,   Jane Rossing

r.neighbors is a good fast way of doing what you what. If your DEM is
exactly 30m n-s and e-w, all you need to do is:

g.region rast=DEM30
g.region res=10
r.neighbors in=DEM30 out=DEM10 method=average size=3

Spelling on my part is always subject to error.

Chuck Ehlschlaeger

Note: results will not be the same as an r.surface using the centers of 
30 meter DEMs but "it will just look a little better".