[GRASS-user] overlapping areas seem valid to v.build: why?

Markus Metz markus.metz.giswork at googlemail.com
Mon Dec 5 03:15:12 EST 2011

Hamish wrote:
> Ben wrote:
>> So from a user point of view, getting rid of "-c" in
>> GRASS 7 would remove another source of uncertainty.
> if that means that tasks like the ones I described
> in the third bullet point of this email:
>  http://lists.osgeo.org/pipermail/grass-user/2011-December/062818.html
> are no longer possible, then I can not support that.
> IMO relying on v.external as work-around to be able to
> deal with that class of data is a bit of a cop-out.

In case of overlapping areas, v.in.ogr assigns multiple categories to
the same centroid, but only if the -c flag is not used. Therefore
extracting areas by category value or where statement may extract
several areas that share the same category. There is your original
polygon. This is not possible if v.in.ogr is used with the -c flag.
IOW, the task refered to above is only possible if v.in.gr does its
cleaning, and not possible if the -c flag is used because the area in
question may not have been built because of corrupt topology. Another
argument for, not against the removal of the -c flag.

Markus M
> Hamish
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