[GRASSLIST:714] Re: Finding overlapping polygons with Grass

[Hamish]

> I need to run several topological operations on a large number of
> polygon shapefiles.

Shell (bash) scripting is your friend. And not so hard to do.

Import shape files with v.in.ogr or maybe fast to connect to them
without importing using v.external. Topology isn't built with v.external
so you might have to use v.in.ogr to import them properly. On the
other hand, v.in.ogr will clean the topology of the shapefiles during
import, and maybe that's not what you want (use the v.in.ogr -c flag)
in this case.

> The first of the operation should be able to isolate overlaps and show
> the polygons contributing to the overlap so that one can check each
> one correct it accordingly.

v.overlay

There's an example on the vector screenshots page: (Overlapping polygons
and v.overlay sections)

http://grass.ibiblio.org/grass60/screenshots/vector.php


> The second operation involves dissolving multi-part polygons.

v.extract -d


> Is there any way to these in grass?

It's not so hard to do,

good luck
Hamish