polygons

[Rick Thompson]

Hi Trond,
  First thing, ensure no previous MASK is set (always a good thing).
  After you have used r.line, v.support as you did, then use v.trim to remove 
spurs at the max length of 100, support again, then use v.alabel -i to 
incrementally give category numbers to the polygons. After this, there will 
still be some spurs and lines present that prevent some polygons from labelling.
Go into v.digit, enter Customize "Enter Display Options Menu" turn on
Area Border lines, then go into Customize "Enter Color Options Menu" and select
yellow of "a", black for "A" and magenta for "h". Once your image displays,
you'll notice that spurs/lines preventing unlabelled polygons from labelling
will be easily noticeable. Remove them, resupport, re- v.alabel -i, then re-
v.to.rast to have your enter area of polygons labelled. Hope this helps. Rick

> I have delineated polygon boundaries from a scanned image and imported
> it into a raster map layer in grass. Then, after using "r.thin" on the
> boundary lines, I converted the polygons to a vector layer using 
> "r.line" with option "type=area". All that worked fine, and I got a map
> layer with 363 lines, 263 nodes, 118 areas and 8 isles. Now, from these
> polygons I want to create a raster map where all the cells within a
> polygon has a certain category value. The result should be a patchy mosaic 
> of polygons with different colors. To achieve this I use "v.support" on the
> converted vector-map to create topology and to assign categories to the
> polygons. Then I use "v.to.rast" to re-convert the polygons from vector to 
> raster format.
------------------------------------------------------------------------
Rick Thompson-   Research Assistant           E-mail: rick at cast.uark.edu
Center for Advanced Spatial Technologies      Telephone: (501) 575-5736
Ozark Hall Rm. 12                             Fax: 575-3846 
University of Arkansas              
Fayetteville, AR 72701