On 31/03/14 15:33, BLANDENIER Lucien wrote:
Hello,
I'm wondering how does r.mapcalc compute the value of a new pixcel if the
resolution have been reduced before (i.e. the pixcel is larger). Is it an
average ?
I did a simple test with a 10*10 pixcel raster. I reduced the resolution to 5*5 and made
a new raster with r.mapcalc "newrast=oldrast*1" but the result was not an
average but the higher value of the four underlying pixcels.
I did then the same operation with a more coarser resulution and it seemed to
be ok.
Could someone explain this?
Short answer: GRASS uses nearest neighbor interpolation as the default
method for resampling.
For more details: http://grass.osgeo.org/grass64/manuals/rasterintro.html
"Resampling methods and interpolation methods"
Moritz
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