[GRASS-user] buffer on granular polygon... it fails

[Hamish]

G. Allegri wrote:
> I'm having a problem trying to execute a buffer of 150m on a polygon
> generated from a raster with resolution 5x5.
> The polygon is a single area, constituted of 1576 vertices (highly
> granular).
> v.buffer generates 32633 vertices, the it get "mad" building the
> topology: it tries to remove intersections, duplicates, etc. giving
> the following final result:
> 
>  Topology was built.
>  Number of nodes     :   32633
>  Number of primitives:   65264
>  Number of points    :   0
>  Number of lines     :   0
>  Number of boundaries:   65264
>  Number of centroids :   0
>  Number of areas     :   32632
>  Number of isles     :   1
>  Number of areas without centroid :   32632
> 
> The vector is not readable...
> 
> I don.t know if the problems is due to the buffer algorithm, which
> fails because of the pixelated polygon (figure below)
> 
>  ____
>       |                          _______
>       |_______             |            |
>                    |            |            |
>                    |_______|            |_______
> 
> I've tried to generilze it, but I get no reduction of the number of
> vertices. I can't figure out why!
> 
>  v.generalize input=grd0_MASKED output=grd0_MASKED_Gen type=area
>  method=douglas_reduction threshold=50 reduction=50
> 
>  Any advice?

v.buffer has some problems,
  http://trac.osgeo.org/grass/ticket/90

It's not a perfect solution but maybe try v.to.rast + r.buffer +
r.to.vect ?


Hamish



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