[GRASS-user] Cropping maps

[Markus Metz]

On Fri, Dec 1, 2017 at 4:26 PM, Vaclav Petras <wenzeslaus at gmail.com> wrote:
>
> For cropping, see also a new addon module called r.clip which clips
according the computational region while respecting mask and the *original*
raster resolution:
>
> https://grass.osgeo.org/grass72/manuals/addons/r.clip.html
>
> Testing and feedback welcome.

About
https://trac.osgeo.org/grass/browser/grass-addons/grass7/raster/r.clip/r.clip.py#L42

g.region align=original

is sufficient. You don't need to specify nsres or ewres when aligning to a
raster map because nsres and ewres of the raster map are used anyway for
alignment.

Markus M
>
> Vaclav
>
> On Tue, Sep 26, 2017 at 10:35 AM, Moritz Lennert <
mlennert at club.worldonline.be> wrote:
>>
>> On 26/09/17 16:17, Moritz Lennert wrote:
>>>
>>> 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.
>>
>>
>> I've rewritten the wiki page to try to make things clearer.
>>
>>
>> Moritz
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>
>
>
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