[GRASS-user] Thiessen Polygons

Glynn Clements glynn at gclements.plus.com
Thu Feb 12 02:00:12 EST 2009


Dylan Beaudette wrote:

> >> >> Does anyone know how to do Thiessen Polygons in GRASS?
> >> >>
> >> >> I need to use them around various types of megalithic tomb
> >> >> sites that are in point vector files.
> >> >
> >> > v.voronoi
> >> >
> >> >
> >> > there is some replacement test code to look at in grass-addons as well:
> >> >  http://trac.osgeo.org/grass/browser/grass-addons/vector/voronoi
> >>
> >> While we are on this topic, is there a way to get a weigthed voronoi
> >> diagram using grass ?
> >>
> >> The ability to rank a point to tune the area's influence would be great,
> >> for that purpose I've been using an arcgis'extension* but with grass it
> >> is not possible**. Is there a way to get a similar result ?
> >>
> >> *http://www.geog.unt.edu/~pdong/software.htm
> >> **http://osdir.com/ml/gis.grass.user/2004-04/msg00036.html
> >>
> >> Regards,
> >> MORREALE Jean Roc
> 
> Now that I have read about 'weighted voronoi diagrams', I wonder if a
> combination of r.cost + r.mapcalc would solve this problem. Something
> along those lines is demonstrated here:
> 
> http://casoilresource.lawr.ucdavis.edu/drupal/node/288
> 
> This example isn't quite what is requested, although using r.cost with
> start=point_i, and stop=neighbor_points (derived from v.delaunay /
> v.distance?) may work. It would then be a little more work to convert
> the weighted-distance rasters into polygons, and link back to the
> original attribute tables... but (hopefully) not outside the realm of
> possibility via a script.

The problem with using r.cost is that you would need to know the cost
for each cell before you have created the polygons.

I think that the simplest accurate approach would be to modify
r.grow.distance.

-- 
Glynn Clements <glynn at gclements.plus.com>


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