[postgis-devel] Minimum number of points in a POLYGON ring?

[Mark Cave-Ayland]

Kevin Neufeld wrote:
> My my readings, according to OGC, the number of points is vague, but the 
> ruleset is specific.  A Polygon is made up of a set of LinearRings 
> (following a set of rules about how they relate to eachother).  A 
> LinearRing is a LineString that is both closed (startpoint ~= endpoint) 
> and simple (does not self-intersect).  This implies that a linear ring 
> must be made up of at least 4 points (3 distinct points) to avoid 
> self-intersection.
> 
> So the parser check should probably be increased the check to 4, but 
> making sure the endpoints are equal (thus 3 distinct points).
> 
> Does that help?

Yes thanks, that was my interpretation of the specification too. However 
please see my reply to Paul's thoughts on loosening the parser checks - 
I'll leave things as they are for the moment until we can come up with 
some form of consensus as to which way we should go.


ATB,

Mark.

-- 
Mark Cave-Ayland
Sirius Corporation - The Open Source Experts
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