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

GRASS GRASS user
1

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.

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?

Thanks
Pierluigi

--

________________________________________________________________________
Ing. Pierluigi De Rosa (PhD)
Studio Associato GFOSSERVICES
                
Presso CAMPUS Via F.lli Cairoli 25 - 06127 Perugia (PG)
fax: 075 7823038
cel: 3497558268
web: www.gfosservices.it
skype: pierluigi.derosa

2

On Mon, Jul 27, 2015 at 9:41 AM, Ing. Pierluigi De Rosa
<pierluigi.derosa@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