Iván Sánchez Ortega wrote:
El día Friday 20 August 2010 13:00:08, Sebastian Klein dijo:
what are valid geometries for closed ways that represent an area?
If you want polygons to behave as in "paleo" GIS, you should refer to the
industry standars. Specifically, to
http://www.opengeospatial.org/standards/sfa , version 1.2.1, page 26:
c) No two Rings in the boundary cross and the Rings in the boundary of a
Polygon may intersect at a Point but only as a tangent, e.g.
∀ P ∈ Polygon, ∀ c1,c2∈P.Boundary(), c1≠c2,
∀ p, q ∈Point, p, q ∈ c1, p ≠ q ,
[p ∈ c2] ⇒ [∃ δ > 0 ∍ [|p-q|<δ] ⇒ [q ∉ c2] ];
I don't really understand this one. The statement is always true since
you can choose δ := |p-q|/2
Do they mean the intersection of 2 boundary rings is always a finite set?
Pay attention to "e": The interior of a polygon is a connected point set. In
your example, the polygon is two connected point sets.
Yes, and the LinarRings are supposed to be simple, which by definition
does not allow self tangency.
P.S.: Don't you just love all those UTF-8 math operators?
You are a genius. :)
Are there any reference algorithms to test for validity?
I remember someone said that "Multipolygon" would be misnomer. But
according to this specification, it fits quite well, doesn't it?
Sebastian
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