reducing grid size of elevation data

[Andrew Hertz]

Hmmm, I was under the impression that GRASS automatically resamples
the data to match the current region settings and then resamples
again to match the display device.  So for display purposes you
shouldn't need to explicitly resample your data layer if
your current region is set to 10m resolution - and you've
d.erase'd :-)  As to what resampling technique is used,
I've found references to nearest neighbor resampling in the
manuals, but it's not entirely clear to me if this is the one
and only technique used.  I hope someone can clarify this...

Which raises an issue I've been wondering about.  If my
understanding is correct, since most of the GRASS routines observe
the region settings, unless all one's data is identical with respect
to the region settings, resampling is being done extensively.
Is this true?
If so, what kinds of error are introduced and how does one
track the error associated with combining, mapcalcing or
otherwise analyzing multiple layers at different resolutions?
If this isn't true then how do r.combine and r.mapcalc process
raster layers with different resolutions?

Andrew Hertz
hertz at geog.psu.edu