do resolution changes effectively average data ?

GRASS GRASS user
1

Hello,

  In grass, if you have a 10 metre grid resolution raster data layer and
you go from 10 metre resolotion to 100 metre resolution using g.region, and then
perform an operation on that raster data layer; - does the opertion occur on an
averaged value from all original 10 metre grid cells in order to produce the new
100 metre grid raster - or does the operation occur only on the top left 10
metre grid cell value within the new 100 metre grid? Or does something else
happen?

  Cheers, Al.

GRASS resamples based on the value of the center cell. If there is no center
cell (as in your example), it would take the value of the upper-left cell
out of the center four, *not* the upper-left cell of the 10 x 10 block.

Not a great explanation; I hope it makes sense!
--
Malcolm D. Williamson - GIS Specialist E-mail: malcolm@cast.uark.edu
Center for Advanced Spatial Technologies Telephone: (501) 575-6159
Ozark Rm. 12 Fax: (501) 575-5218
University of Arkansas
Fayetteville, AR 72701

2

Malcolm Williamson (malcolm@cast.uark.edu) writes on 18 Jan 95:

GRASS resamples based on the value of the center cell. If there is no center
cell (as in your example), it would take the value of the upper-left cell
out of the center four, *not* the upper-left cell of the 10 x 10 block.

see also ftp://pasture.ecn.purdue.edu/pub/mccauley/grass/s.sample.tar.gz
and http://soils.ecn.purdue.edu/~aggrass/html4/s.sample.html for info on
sampling rasters at site locations using nearest neighbor, bilinear
interpolation, and cubic convolution.

--Darrell
James Darrell McCauley, USDA National Needs Fellow
Agric Engineering, Purdue University, West Lafayette, IN 47907-1146, USA
mccauley@ecn.purdue.edu +++ http://soils.ecn.purdue.edu/~mccauley/