[postgis-devel] isvalid() error

[Markus Schaber]

Hi, Strk,

strk at refractions.net schrieb:

>>>PostGIS always allowed polygon rings with 3 points.
>>>In this case it disagrees with GEOS about this.

The reason is that GEOS needs three _distinct_ points. As the ring has
to be closed, four coordinate pairs have to be given, whereas the last
one equals the first one.

> Question is: can we safely have GEOS accept them ?
>
> I belive both SnapToGrid() and Simplify() also produce 3points rings ...

Such a 3 point ring is actually "collapsed" to a line which has no area.
As Polygons describe areas, maybe such shapes should be dropped altogether.

Markus
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