Thanks for the advice.
I am thinking that since these are rounding problems, it is likely that
those self-intersections will be just pairs of flipped points very close to
each other.
Isn't there a simple way of detecting them and than just flipping their
order in polygon?
On Mon, Jan 25, 2016 at 9:10 PM Martin Davis <[email protected]> wrote:
> Thanks for the issue report.
>
> it is liikely to be too difficult/non-performant to enhance EarClipper to
> handle invalid inputs. So I recommend checking the input for validity.
>
> It can be tricky to fix invalid polygons. It's better to avoid creating
> invalid geometry in the first place. There's some code in the JTS Lab that
> uses snap-rounding to accomplish this [1].
>
> [1]
> http://sourceforge.net/p/jts-topo-suite/code/HEAD/tree/trunk/jts-lab/src/main/java/com/vividsolutions/jtslab/SnapRoundOverlayFunctions.java
>
> On Mon, Jan 25, 2016 at 12:01 PM, Stanisław Góra <[email protected]>
> wrote:
>
>> Hi,
>> First of all, thank you for sharing this code with me.
>> Yes, I still can't subscribe, but since I got in contact with you, it
>> isn't that big of a problem.
>> I tested all four versions but if I understand correctly EarClip and
>> EarClipperO are the older ones. EarClipper is working much faster - don't
>> see any more performance issues.
>> (In my app I am triangulating some polygons each screen refresh to draw
>> them)
>> However after some time running my java app started Not Responding.
>> After investigating my input I found out that when app generate incorrect
>> (self-intersecting) polygon like these:
>> POLYGON ((5670 4363, 6465 2509, 6458 2500, 5670 4364, 5670 4363))
>> POLYGON ((8235 3680, 7868 3610, 7454 3890, 7360 4381, 7640 4795, 7763
>> 4818, 7821 4679, 7821 4680, 7535 4213, 7891 3796, 8144 3901, 8235 3680))
>> through some robustness issue in previously used intersection() - it
>> happens randomly,
>> EarClipper hangs app. I've done ThreadDump and found specific line:
>>
>> "LWJGL Application" #15 prio=5 os_prio=0 tid=0x000000001911a800
>> nid=0x1be0 runnable [0x000000001d73e000]
>> java.lang.Thread.State: RUNNABLE
>> at
>> com.vividsolutions.jts.polytriangulate.EarClipper.computeEars(EarClipper.java:116)
>> at
>> com.vividsolutions.jts.polytriangulate.EarClipper.triangulate(EarClipper.java:80)...
>>
>> I suppose I haven't done proper stress testing because I usually have
>> from 5 to 30 points in polygon. Can you make a fix to ear clip algorithm or
>> should I do an extra check for my polygons? If so how would you recommend
>> fixing them using jts?
>> Thanks
>>
>> On Sun, Jan 24, 2016 at 12:30 AM Martin Davis <[email protected]> wrote:
>>
>>> Have a look at this - this is the code that is intended to wind up in
>>> JTS at some point. Feedback welcome.
>>>
>>> https://github.com/dhtong/jts/tree/master/src/polytriangulate
>>>
>>> Not sure about the subscribe issue - is it still happening?
>>>
>>> On Sat, Jan 23, 2016 at 5:37 AM, Stanisław Góra <[email protected]>
>>> wrote:
>>>
>>>> Hi,
>>>>
>>>> I am looking for a best way to triangulate polygons using JTS. Since it
>>>> does not have Constrained Delaunay implementation (which would really help
>>>> me) i looked at using Conforming Delaunay and setting constraints. Then i
>>>> needed to get rid of the triangles that lie outside (concave) polygons and
>>>> inside their holes. Testing each triangle with disjoint() and covers()
>>>> functions takes much longer than triangulation itself and doesn't even
>>>> produce reliable results because of some robustness issue. (triangles
>>>> around added Steiner points lying on constrained segments return incorrect
>>>> inside/outside polygon result).
>>>> Then I found this thread
>>>> http://sourceforge.net/p/jts-topo-suite/mailman/jts-topo-suite-user/thread/[email protected]/
>>>> and
>>>> tried Michael's Ear Clipping code. It does great job at triangulating
>>>> polygons but is a lot slower (92% time is spent on covers() function) and
>>>> is killing performance on a android device even more than delaunay.
>>>>
>>>> In this article
>>>> http://lin-ear-th-inking.blogspot.com/2011/04/polygon-triangulation-via-ear-clipping.html
>>>> Martin
>>>> Davis said that the Ear Clipping code will get added to JTS in the next
>>>> release, and while it didn't maybe it was further optimized.
>>>> Also, are there any plans to implement Constrained Delaunay? I realized
>>>> I can't use Conforming Delaunay for yet another reason: I have some very
>>>> long rectangle-like polygons to triangulate, which forces delaunay property
>>>> to generate countless small triangles and produces "Too many splitting
>>>> iterations" error.
>>>> Otherwise can You point me to a fastest (runtime) way of triangulating
>>>> polygons using either Conforming Delaunay or Ear Clipping given my
>>>> problems?
>>>>
>>>> Thank You very much,
>>>> Stanisław Góra
>>>>
>>>> PS. It seems I'm unable to subscribe jts user list - getting "Bug in
>>>> Mailman version 2.1.9"
>>>>
>>>>
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