[GRASS-user] r.mapcalc and g.region

[Moritz Lennert]

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