[GRASS-user] Apply "v.transform" in polygons with overlays

[Markus Metz]

On Tue, Feb 26, 2013 at 2:36 PM, Jose M Michia Roberts
<jose.maria.michia at gmail.com> wrote:
> 2013/2/26 Benjamin Ducke <benducke at fastmail.fm>:
>> A "fix" might be to introduce a new GRASS env
>> variable that can be set to suppress the cleaning
>> functions. While it would probably be trivial to
>> implement this, it would also break with GRASS'
>> basic design and the assumptions that its vector
>> processing modules make (namely that the input
>> data is topologically correct).
>
> Yes, I know. But I think that there are some cases, like this, where
> the overlaps between polygons are part of the information and need to
> be preserved.

The overlaps between polygons are only preserved if you do not use the
-c flag for v.in.ogr. Each original polygon can then be recreated with
v.extract -d cat=X. If you use the -c flag with v.in.ogr, you are on
your own.

BTW, v.transform simply transforms coordinates, it does not do any
cleaning. v.transform should actually work without topology, building
topology on the output is optional (in GRASS 7).

>
> And I understand that a situation like this would limit the
> application of other modules.
>
> Maybe I'm totally wrong: I still have so much to study about GRASS!

For this particular problem (georectifying overlapping polygons) there
is probably an easier solution outside GRASS. Maybe QGIS supports
coordinate transformation/rectification using GCPs?

Markus M


> (english too... right?) :D
>
> Thanks,
> Jose
> _______________________________________________
> grass-user mailing list
> grass-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user