There's no code in JTS to do this.
I guess the algorithm would be to inspect triples of segments and flip the
middle segment if the ends intersect.
On Mon, Jan 25, 2016 at 12:26 PM, Stanisław Góra <[email protected]> wrote:
> 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"
>>>>>
>>>>>
>>>>> ------------------------------------------------------------------------------
>>>>> Site24x7 APM Insight: Get Deep Visibility into Application Performance
>>>>> APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month
>>>>> Monitor end-to-end web transactions and take corrective actions now
>>>>> Troubleshoot faster and improve end-user experience. Signup Now!
>>>>> http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140
>>>>> _______________________________________________
>>>>> Jts-topo-suite-user mailing list
>>>>> [email protected]
>>>>> https://lists.sourceforge.net/lists/listinfo/jts-topo-suite-user
>>>>>
>>>>>
>>>>
>>
------------------------------------------------------------------------------
Site24x7 APM Insight: Get Deep Visibility into Application Performance
APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month
Monitor end-to-end web transactions and take corrective actions now
Troubleshoot faster and improve end-user experience. Signup Now!
http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140
_______________________________________________
Jts-topo-suite-user mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/jts-topo-suite-user
