[geos-devel] [GEOS] #588: valid polygon when cw, not valid when ccw

[Martin Davis]

Yes, JTS has the problem too.  Sigh....  I'll have to dig into it to 
find out why this is failing.  I made some improvements to the 
orientation test recently which I thought would make it fully robust, 
but perhaps there's still issues.  Or else something else is going on....

On 9/12/2012 3:14 AM, GEOS wrote:
> #588: valid polygon when cw, not valid when ccw
> ------------------------+---------------------------------------------------
>   Reporter:  olivier80   |       Owner:  geos-devel@…
>       Type:  defect      |      Status:  new
>   Priority:  major       |   Milestone:  3.3.6
> Component:  Default     |     Version:  3.3.5
>   Severity:  Unassigned  |    Keywords:
> ------------------------+---------------------------------------------------
>
> Comment(by strk):
>
>   The polygon ring has 7 points, but it's a 4 sides polygon. So 2 vertices
>   are very close to other vertices.
>
>   I'd love to have a function (in postgis) to analyze these cases and answer
>   questions like: what's the minimum distance between two consecutive
>   vertices ? what's the minimum distance between any two vertices ?
>
>   Simplifying the geometry with a tolerance of 1e-10 is enough to fix the
>   invalidity, but anyway the robustness problem exists. I didn't try with
>   JTS but I suspect it may be an issue there as well.
>