reducing grid size of elevation data

[Jim Aanstoos (919) 541-6890]

>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

If what you are looking for is simply a smoothed version of the
data (when viewed at higher sampling rates), then r.neighbors
using the "average" function should give you what you are looking
for.  You'll have to change the resolution in your current region
setting to the desired 10m figure before running it.
Alternatively, you could use the more flexible (for filtering
applications) r.mfilter and design your own smoothing filter.
I have used r.mfilter, for other purposes, and it works fine.

I've often thought that it might be nice if the r.resample
program, which currently only uses nearest-neighbor resampling,
offered other options as well (such as bilinear, cubic
convolution, etc.).  Of course, those other resampling techniques are
not appropriate for all GIS raster data-- but for image data and
even elevation data, especially for viewing purposes, they can be
useful.
            /\
      jim  /--\
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______________________________________________________________________
Jim Aanstoos                      Internet: aanstoos%louie at rcc.rti.org
                                         or aanstoos%louie at rti.rti.org
Research Triangle Institute                                           
PO Box 12194                                       Phone: 919-541-6890
Research Triangle Park, NC 27709-2194                Fax: 919-541-6515
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