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

[Markus Metz]

On Fri, Dec 2, 2011 at 12:43 PM, Maris Nartiss <maris.gis at gmail.com> wrote:
> Pardon my ignorance,
> how is possible to distinguish areas without centroids from holes?
> And why it doesn't make sense?

A hole is a nothing in a something. If there is no something all
around the hole there is no hole. IOW, an area without a centroid is a
hole if it is completely surrounded by other areas with centroids,
otherwise that area is not a hole because it shares one or more
boundaries with the outer void. This does not make sense logically
because then there are two indistinguishable voids bordering each
other. These two voids can just as well be combined into one, lest
there is something special about one of the two voids, but that you
could only tell if there is a centroid in one void, rendering it
non-void.

Markus M
>
> Maris,
> just finished converting and cleaning CAD (spaghetti) lines + points
> to valid areas.
>
> 2011/12/2 Markus Metz <markus.metz.giswork at googlemail.com>:
>>
>>  * for areas without centroids that are not holes. Areas without
>> centroids that are not holes are topologically correct but do not make
>> sense logically.