[GRASS-user] Cropping maps

[Moritz Lennert]

On 26/09/17 15:57, Marco Alicera wrote:
> Dear list,
> I am trying to crop a raster map into a smaller area, but I am failing.
> 
> This wiki page link <https://grasswiki.osgeo.org/wiki/Cropping_maps> is 
> quite clear:
> "Make boundary into mask using r.mask 
> <https://grass.osgeo.org/grass72/manuals/r.mask.html> then copy raster 
> source to new map (g.copy 
> <https://grass.osgeo.org/grass72/manuals/g.copy.html>). All cells 
> outside of the mask will be omitted from the new copy."
> 
> r.mask vector=myarea
> g.copy --overwrite raster=OldRasterWithBigArea,NewRasterWithSmallArea
> r.mask -r
> 
> I expected all cell outside were not going to be omitted, but replaced 
> by NULL.

I'm not sure I understand your last sentence, but AFAIK, the wiki info 
is wrong. g.copy works directly on the files and ignores mask and region 
settings. In your example, OldRasterWithBigArea and 
NewRasterWithSmallArea should be strictly identical.

You need to use r.mapcalc "new = old" while the mask is set to get a 
raster with everything outside the mask set to NULL.

Moritz