[GRASS5] Overlapping polygons

[Radim Blazek]

Hi,

I have enabled to add more categories of the same field 
to one geometry element. In other words, geometry may be linked
to 0, 1 or more records in the same table. This one-to-many
relation between geometry and attribute table gives a possibility
to create overlapping polygons in one vector map. 

There are 2 kinds of data with overlapping polygons:
1) Overlaps are errors in data
2) Overlaps are correct; polygons differ in 3. dimension - time or z coordinate
   (forest fire, overpass, tunel) or in attribute (animal's territory)

Practical consequences:
Overlapping polygons can be now imported to GRASS without any error 
and without any loss of information. Overlaps may be then used in analysis
or easily identified as wrong data or simply ignored (and get wrong results
from wrong input without troubles).

Until now, I have modified v.in.ogr, d.vect, v.digit and v.to.db
to use this feature.

Example: http://mpa.itc.it/radim/g51/index.html#fire

Radim