[GRASS-user] confused on categories created by topological cleaning of overlapping polygons

G. Allegri giohappy at gmail.com
Tue Nov 29 16:00:34 EST 2011

I'm still assessing the topological model and the build/clean effects on
various combinations of synthetic geometries created by myself.
This time I have created two overlapping polygons [1] [2] in Qgis, and
imported in grass thorugh v.in.ogr.

If I import the shapefile with the clean tool activated, I obtain 3 areas:
two with one category and one layer, the other one (the overlapping zone)
has two layers [3]:

layer 1: category 1/2
layer 2: category 1

BUT, the two layers appear only if I display the categories with v.digit.
All the other tools list only one layer (the one in common with the other
two areas).
This leads to various problems:

 - the wxGUI (the identify tool inside the display window crashes)
 - to remove the layer 2, because layer 2 isn't selectable from the other
modules (like v.category, etc.)
 - to remove the second category from layer 1 I still have to use v.digit
because neither v.edit nor v.category let me choose the category number I
want to mantain/remove.

Is this the expected behaviour of overlapping regions cleaning?


[1] image: http://www.giovanniallegri.it/share/test_polygon.png
[2] shapefile: http://www.giovanniallegri.it/share/test_polygon.zip
[3] http://www.giovanniallegri.it/share/cleaned_test_polygon.png
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