[GRASSLIST:583] Re:

[lponti at infinito.it]

Thanks David:
Your idea is something I had not thought to. The more I 
use GRASS, the better I appreciate r.mapcalc.

Thanks again Stefano:
I looked at v.voronoi and it seems to get exactly the 
buffer area I wanted. Voronoi polygons are also an 
interesting geometric concept that I did not know about.

Luigi



On Tue, 4 Apr 2006 22:58:21 -0700
  "David Finlayson" <david.p.finlayson at gmail.com> wrote:
> If white == 1 and black == 0 and you want all the 
>"green" area
> half-way between the white point and the black point, 
>why don't you
> try selecting all areas "green" >= 0.5?
> 
> Step 1: interpolate raster
> Step 2: r.mapcalc "test = if(green >= 0.5, green, 
>null())"
> 
> Alternatively, you could buffer the white points by some 
>reasonable
> distance and select for all cells within X meters of the 
>white point.
> 
> David
> 
> On 4/4/06, lponti at infinito.it <lponti at infinito.it> 
>wrote:
>> Dear list,
>>
>> so far, I have been masking either via MASK or 
>>r.mapcalc.
>> This way, only cells corresponding to MASK would display
>> in the masked raster.
>>
>> In contrast, now I would like cells corresponding to a
>> "mask" NOT to display* in the main raster layer. Is 
>>there
>> a way to do it?
>>
>> This is part of a larger issue I am addressing and that 
>>I
>> will briefly describe. In the attached sample image, you
>> see points imported via v.in.ascii and used to get the
>> green interpolated raster. Values at black points are
>> greater than zero, whereas the value of the white point 
>>is
>> zero (and it is not used for interpolation since it has 
>>no
>> biological meaning).
>>
>> The end result would be to clip out a portion of the 
>>green
>> raster around the white point. This portion would be
>> delimited by midpoints between the white point and the
>> closest neighboring black points.
>>
>> So far, I have been trying to get a vector buffer around
>> the white point and then v.to.rast for some kind of
>> subsequent clipping (described above*). However I have 
>>no
>> cue on how to get a comlex shape from neighboring points
>> as described. Is there a method already in place to do
>> this?
>>
>> Many thanks in advance and any hints much appreciated,
>>
>> Luigi
>>
>> grass6/cygwin user
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>>
>>
>>
>>
>>
>>
> 
> 
> --
> David Finlayson

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