[GRASS-user] Clipping rasters

[Jarek Jasiewicz]

Hanlie Pretorius pisze:
> 2010/8/10, Nikos Alexandris <nikos.alexandris at felis.uni-freiburg.de>:
>   
>> Hanlie Pretorius wrote:
>>
>>     
>>> I thought I created a clipped DEM by rasterising an irregular vector
>>> boundary and then using a mask to create the clipped DEM from a
>>> rectangular DEM.
>>>
>>> For example:
>>> -----
>>>       
>> #first, check and set your region of interest
>> g.region vect=border -pa
>>     
>
> Tried this with the same result, as Jarek points out in the second
> reply. So, I assume it's impossible to have a raster with an irregular
> boundary in GRASS?
>
>   
>>> # convert vector border to raster
>>> v.to.rast input="border" output="border" use="cat" type="area" layer=1
>>> value=1 rows=4096                                |
>>>
>>> # set the mask to the raster border
>>> r.mask border
>>>       
>>> # create the clipped DEM
>>> r.mapcalc
>>>
>>>       
>>>> dem_clipped=dem_full
>>>>         
>>> # remove the mask
>>> r.mask -r
>>> -----
>>>
>>> But it turns out I was wrong, the 'clipped' raster just contains NULL
>>> values outside of the border raster. What did I do wrong? Is there a
>>> better way to clip a raster to a vector boundary?
>>>       
>> So, always check the region ;-). I think this is the best (and only?) way to
>> clip.
>>
>> Regards, Nikos
>>
>>     
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>   
raster is a matrix of values so it is always rectangular. Null is not a 
value, NULL is lack of value. Irregular raster is a rectangural raster 
with null (transparent) cells outside the border
J.