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From "Luc Maisonobe (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (MATH-880) Polygon difference produces erronious results in some cases
Date Wed, 17 Oct 2012 14:44:03 GMT
```
[ https://issues.apache.org/jira/browse/MATH-880?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13477922#comment-13477922
]

Luc Maisonobe commented on MATH-880:
------------------------------------

I confirm the issue.

The null points probably come from the algorithm thinking some boundaries are not closed,
i.e. they extend to infinity. This is the way they are represented when transforming from
BSP to boundary representation. So the problem is not the nul points by themselves, but trather
why the algorithm fails to see the boundary should remain closed here.

There is probably a numerical problem here. It will require some investigations.

> Polygon difference produces erronious results in some cases
> -----------------------------------------------------------
>
>                 Key: MATH-880
>                 URL: https://issues.apache.org/jira/browse/MATH-880
>             Project: Commons Math
>          Issue Type: Bug
>    Affects Versions: 3.0
>            Reporter: Curtis Jensen
>             Fix For: 3.1
>
>         Attachments: PolygonDiffAll.png, PolygonDiffResults.png, PolygonInputs.png
>
>
> The 2D polygon difference method is returning incorrect
> results.  Below is a test case of subtracting two polygons (Sorry,
> this is the simplest case that I could find that duplicates the
> problem).
> There are three problems with the result. The first is that the first
> point of the first set of vertices is null (and the first point of the
> second set is also null).  The second is that, even if the first null
> points are ignored,  the returned polygon is not the correct result.
> The first and last points are way off, and the remaining points do not
> match the original polygon boundaries.  Additionally, there are two
> holes that are returned in the results.  This subtraction case should
> not have holes.
> {code:title="Complex Polygon Difference Test"}
> public void testComplexDifference() {
>         Vector2D[][] vertices1 = new Vector2D[][] {
>             new Vector2D[] {
>                     new Vector2D( 90.08714908223715,  38.370299337260235),
>                     new Vector2D( 90.08709517675004,  38.3702895991413),
>                     new Vector2D( 90.08401538704919,  38.368849330127944),
>                     new Vector2D( 90.08258210430711,  38.367634558585564),
>                     new Vector2D( 90.08251455106665,  38.36763409247078),
>                     new Vector2D( 90.08106599752608,  38.36761621664249),
>                     new Vector2D( 90.08249585300035,  38.36753627557965),
>                     new Vector2D( 90.09075743352184,  38.35914647644972),
>                     new Vector2D( 90.09099945896571,  38.35896264724079),
>                     new Vector2D( 90.09269383800086,  38.34595756121246),
>                     new Vector2D( 90.09638631543191,  38.3457988093121),
>                     new Vector2D( 90.09666417351019,  38.34523360999418),
>                     new Vector2D( 90.1297082145872,  38.337670454923625),
>                     new Vector2D( 90.12971687748956,  38.337669827794684),
>                     new Vector2D( 90.1240820219179,  38.34328502001131),
>                     new Vector2D( 90.13084259656404,  38.34017811765017),
>                     new Vector2D( 90.13378567942857,  38.33860579180606),
>                     new Vector2D( 90.13519557833206,  38.33621054663689),
>                     new Vector2D( 90.13545616732307,  38.33614965452864),
>                     new Vector2D( 90.13553111202748,  38.33613962818305),
>                     new Vector2D( 90.1356903436448,  38.33610227127048),
>                     new Vector2D( 90.13576283227428,  38.33609255422783),
>                     new Vector2D( 90.13595870833188,  38.33604606376991),
>                     new Vector2D( 90.1361556630693,  38.3360024198866),
>                     new Vector2D( 90.13622408795709,  38.335987048115726),
>                     new Vector2D( 90.13696189099994,  38.33581914328681),
>                     new Vector2D( 90.13746655304897,  38.33616706665265),
>                     new Vector2D( 90.13845973716064,  38.33650776167099),
>                     new Vector2D( 90.13950901827667,  38.3368469456463),
>                     new Vector2D( 90.14393814424852,  38.337591835857495),
>                     new Vector2D( 90.14483839716831,  38.337076122362475),
>                     new Vector2D( 90.14565474433601,  38.33769000964429),
>                     new Vector2D( 90.14569421179482,  38.3377117256905),
>                     new Vector2D( 90.14577067124333,  38.33770883625908),
>                     new Vector2D( 90.14600350631684,  38.337714326520995),
>                     new Vector2D( 90.14600355139731,  38.33771435193319),
>                     new Vector2D( 90.14600369112401,  38.33771443882085),
>                     new Vector2D( 90.14600382486884,  38.33771453466096),
>                     new Vector2D( 90.14600395205912,  38.33771463904344),
>                     new Vector2D( 90.14600407214999,  38.337714751520764),
>                     new Vector2D( 90.14600418462749,  38.337714871611695),
>                     new Vector2D( 90.14600422249327,  38.337714915811034),
>                     new Vector2D( 90.14867838361471,  38.34113888210675),
>                     new Vector2D( 90.14923750157374,  38.341582537502575),
>                     new Vector2D( 90.14877083250991,  38.34160685841391),
>                     new Vector2D( 90.14816667319519,  38.34244232585684),
>                     new Vector2D( 90.14797696744586,  38.34248455284745),
>                     new Vector2D( 90.14484318014337,  38.34385573215269),
>                     new Vector2D( 90.14477919958296,  38.3453797747614),
>                     new Vector2D( 90.14202393306448,  38.34464324839456),
>                     new Vector2D( 90.14198920640195,  38.344651155237216),
>                     new Vector2D( 90.14155207025175,  38.34486424263724),
>                     new Vector2D( 90.1415196143314,  38.344871730519),
>                     new Vector2D( 90.14128611910814,  38.34500196593859),
>                     new Vector2D( 90.14047850603913,  38.34600084496253),
>                     new Vector2D( 90.14045907000337,  38.34601860032171),
>                     new Vector2D( 90.14039496493928,  38.346223030432384),
>                     new Vector2D( 90.14037626063737,  38.346240203360026),
>                     new Vector2D( 90.14030005823724,  38.34646920000705),
>                     new Vector2D( 90.13799164754806,  38.34903093011013),
>                     new Vector2D( 90.11045289492762,  38.36801537312368),
>                     new Vector2D( 90.10871471476526,  38.36878044144294),
>                     new Vector2D( 90.10424901707671,  38.374300101757),
>                     new Vector2D( 90.10263482039932,  38.37310041316073),
>                     new Vector2D( 90.09834601753448,  38.373615053823414),
>                     new Vector2D( 90.0979455456843,  38.373578376172475),
>                     new Vector2D( 90.09086514328669,  38.37527884194668),
>                     new Vector2D( 90.09084931407364,  38.37590801712463),
>                     new Vector2D( 90.09081227075944,  38.37526295920463),
>                     new Vector2D( 90.09081378927135,  38.375193883266434)
>             }
>         };
>         PolygonsSet set1 = buildSet(vertices1);
>         Vector2D[][] vertices2 = new Vector2D[][] {
>             new Vector2D[] {
>                     new Vector2D( 90.13067558880044,  38.36977255037573),
>                     new Vector2D( 90.12907570488,  38.36817308242706),
>                     new Vector2D( 90.1342774136516,  38.356886880294724),
>                     new Vector2D( 90.13090330629757,  38.34664392676211),
>                     new Vector2D( 90.13078571364593,  38.344904617518466),
>                     new Vector2D( 90.1315602208914,  38.3447185040846),
>                     new Vector2D( 90.1316336226821,  38.34470643148342),
>                     new Vector2D( 90.134020944832,  38.340936644972885),
>                     new Vector2D( 90.13912536387306,  38.335497255122334),
>                     new Vector2D( 90.1396178806582,  38.334878075552126),
>                     new Vector2D( 90.14083049696671,  38.33316530644106),
>                     new Vector2D( 90.14145252901329,  38.33152722916191),
>                     new Vector2D( 90.1404779335565,  38.32863516047786),
>                     new Vector2D( 90.14282712131586,  38.327504432532066),
>                     new Vector2D( 90.14616669875488,  38.3237354115015),
>                     new Vector2D( 90.14860976050608,  38.315714862457924),
>                     new Vector2D( 90.14999277782437,  38.3164932507504),
>                     new Vector2D( 90.15005207194997,  38.316534677663356),
>                     new Vector2D( 90.15508513859612,  38.31878731691609),
>                     new Vector2D( 90.15919938519221,  38.31852743183782),
>                     new Vector2D( 90.16093758658837,  38.31880662005153),
>                     new Vector2D( 90.16099420184912,  38.318825953291594),
>                     new Vector2D( 90.1665411125756,  38.31859497874757),
>                     new Vector2D( 90.16999653861313,  38.32505772048029),
>                     new Vector2D( 90.17475243391698,  38.32594398441148),
>                     new Vector2D( 90.17940844844992,  38.327427213761325),
>                     new Vector2D( 90.20951909541378,  38.330616833491774),
>                     new Vector2D( 90.2155400467941,  38.331746223670336),
>                     new Vector2D( 90.21559881391778,  38.33175551425302),
>                     new Vector2D( 90.21916646426041,  38.332584299620805),
>                     new Vector2D( 90.23863749852285,  38.34778978875795),
>                     new Vector2D( 90.25459855175802,  38.357790570608984),
>                     new Vector2D( 90.25964298227257,  38.356918010203174),
>                     new Vector2D( 90.26024593994703,  38.361692743151366),
>                     new Vector2D( 90.26146187570015,  38.36311080550837),
>                     new Vector2D( 90.26614159359622,  38.36510808579902),
>                     new Vector2D( 90.26621342936448,  38.36507942500333),
>                     new Vector2D( 90.26652190211962,  38.36494042196722),
>                     new Vector2D( 90.26621240678867,  38.365113172030874),
>                     new Vector2D( 90.26614057102057,  38.365141832826794),
>                     new Vector2D( 90.26380080055299,  38.3660381760273),
>                     new Vector2D( 90.26315345241,  38.36670658276421),
>                     new Vector2D( 90.26251574942881,  38.367490323488084),
>                     new Vector2D( 90.26247873448426,  38.36755266444749),
>                     new Vector2D( 90.26234628016698,  38.36787989125406),
>                     new Vector2D( 90.26214559424784,  38.36945909356126),
>                     new Vector2D( 90.25861728442555,  38.37200753430875),
>                     new Vector2D( 90.23905557537864,  38.375405314295904),
>                     new Vector2D( 90.22517251874075,  38.38984691662256),
>                     new Vector2D( 90.22549955153215,  38.3911564273979),
>                     new Vector2D( 90.22434386063355,  38.391476432092134),
>                     new Vector2D( 90.22147729457276,  38.39134652252034),
>                     new Vector2D( 90.22142070120117,  38.391349167741964),
>                     new Vector2D( 90.20665060751588,  38.39475580900313),
>                     new Vector2D( 90.20042268367109,  38.39842558622888),
>                     new Vector2D( 90.17423771242085,  38.402727751805344),
>                     new Vector2D( 90.16756796257476,  38.40913898597597),
>                     new Vector2D( 90.16728283954308,  38.411255399912875),
>                     new Vector2D( 90.16703538220418,  38.41136059866693),
>                     new Vector2D( 90.16725865657685,  38.41013618805954),
>                     new Vector2D( 90.16746107640665,  38.40902614307544),
>                     new Vector2D( 90.16122795307462,  38.39773101873203)
>             }
>         };
>         PolygonsSet set2 = buildSet(vertices2);
>         PolygonsSet set  = (PolygonsSet) new
> RegionFactory<Euclidean2D>().difference(set1.copySelf(),
>               set2.copySelf());
>         Vector2D[][] verticies = set.getVertices();
>         Assert.assertTrue(verticies[0][0] != null);
>         Assert.assertEquals(1, verticies.length);
>     }
> {code}

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