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

Markus Metz markus.metz.giswork at googlemail.com
Fri Dec 2 03:16:34 EST 2011

Moritz Lennert wrote:
> On 30/11/11 18:37, Markus Metz wrote:
>> Moritz Lennert wrote:
>>> On 30/11/11 14:38, Markus Metz wrote:
>>>> It seems to me that the confusion arises because you made use of
>>>> features that allow you to skip topological cleaning which is not the
>>>> default and not recommended.
>>> Maybe this calls for a v.check.topology module ? Or an option in v.build
>>> or
>>> v.clean which does that (i.e. just check, not clean) ?
>> Good idea. I would opt for a new option/flag for v.build, which can
>> already provide rather detailed diagnostics, e.g. dumping topology.
>> Something like v.build -e for extended topology checks?
> +1
> Now the question is: which checks should be performed ?

Existing checks report the number of incorrect boundaries, duplicate
centroids and centroids outside areas. These are quick and easy to

I would suggest to add new checks
 * for intersecting boundaries indicating duplicate boundaries and/or
overlapping areas
 * for boundaries and lines of zero length (not sure how much harm
zero length boundaries do but it's safer to have them removed)
 * for areas without centroids that are not holes. Areas without
centroids that are not holes are topologically correct but do not make
sense logically.

There are probably special cases not captured with all these checks,
but additional checks could be added later on.

Markus M

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