[GRASS-user] voronoi for polygons

[Martin Rutzinger]

hi martin!

i'm not sure what is wrong with v.select, but i can show a second approach how
to derive voronoi polygons (restriction: doesn't work for adjacent polygons):

- convert the selected polygons to raster (v.to.rast)
- switch null() values to 1 and pixels with values to null() (r.mapcalc)
- thin raster (r.thin) several iterations
- convert thinned raster to vector and make polygons (r.to.vect,...)

this works for me
/martin


********************
Hello,

I want to calculate voronoi areas for polygons, but I am stuck in
the "query-part".

using spearfish data I did:

v.extract input=fields at PERMANENT output=fields_extract list=41,36,46,21

v.to.points input=fields_extract output=fields_extract_points type=boundary

v.voronoi input=fields_extract_points output=fields_extract_points_voron


now I wanted to
- group all voronoi polygons which belong to points of one polygon (GIS query
overlap)
- calculate area of merged voronoi polygons and assign them to each original
polygon

but:

v.select operator=overlap gives:

v.select binput=fields_extract_points_voron_clean ainput=fields_extract_clean
atype=area btype=area output=test operator=overlap
Processing ainput areas ...
 100%
Writing attributes ...
Layer 1
v.select complete.
Building topology ...
0 primitives registered
0 areas built
0 isles built
Attaching islands:
Attaching centroids: Topology was built.
Number of nodes     :   0
Number of primitives:   0
Number of points    :   0
Number of lines     :   0
Number of boundaries:   0
Number of centroids :   0
Number of areas     :   0
Number of isles     :   0

anything wrong with the command?
I did it as well without b/atype=area but same result.

The problem how to calculate areas is not yet tackled ,-)

I appreciate any hint, Martin

________________________________________________________________________________

Mag. Martin Rutzinger

rutzinger at alps-gmbh.com
alpS - Natural Hazard Management
http://www.alps-gmbh.com

martin.rutzinger at uibk.ac.at
Institute for Geography, University of Innsbruck
http://geowww.uibk.ac.at