[GRASS-user] Extract polygon in layer 1 with query on layer 2

[Markus Neteler]

On Mon, Jul 27, 2015 at 9:41 AM, Ing. Pierluigi De Rosa
<pierluigi.derosa at gfosservices.it> wrote:
> Dear All,
>
> I have shapefile with many topology errors. Most of there are
> overlapping area.
> When I'm import in GRASS It create, for all overlapped areas a link in
> layer 2 and in layer 1 it create two category for each centroid.

You mean something like this:
http://grasswiki.osgeo.org/wiki/Vector_topology_cleaning#Polygon_import_from_SHAPE_file

> It is possible extract only areas where each centroid are linked to only
> one category or extract only areas where no link to layer 2 exist?

I see
http://grasswiki.osgeo.org/wiki/Vector_Database_Management#The_concept_of_categories
http://grass.osgeo.org/grass70/manuals/v.in.ogr.html#overlapping-polygons

and darkly remember that this has been discussed but cannot find it.
Perhaps use v.category with option=sum and then v.to.db to transfer it
to the attribute table for filtering?

Please let us know if that works for you (and how). Could be added to
the Wiki then.

best
Markus