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

[Martin Davis]

Turns out that this isn't an issue in the trunk version of JTS (but it 
is in JST 1.12).

This is probably due to the recent switch to using extended precision to 
compute determinant signs - which affects all intersection 
computations.  It would be good if GEOS switched to using this new more 
(fully?) robust technique as well.

On 9/12/2012 7:25 AM, Martin Davis wrote:
> 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.
>>
>
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