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

[Markus Metz]

Markus Metz wrote:
> 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
> catch.
>
> 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.
>

Additional tests for corrupt topology are now in trunk r49553. Please
try v.build -e.

Markus M