[GRASS-user] polygons and centroids

[Markus Metz]

Dave Roberts wrote:
> Friends,
>
>   If I understand correctly (based on experience with my own data), when
> GRASS calculates the topology for vector area data it doesn't actually
> ensure that the centroid lies within the area it represents. If the area is
> a torus, or at least hollow in a general way, then the centroid might
> actually lie in the void in the center of the polygon rather than within the
> interior of the polygon itself.

No, grass does ensure that a centroid lies within an area when
building topology (attaching centroids). After building full topology,
the number of centroids outside any area is reported as
Number of centroids outside area:

Markus M