Please help! Any advice or solutions gratefully received!
I have a simple valid polygon that produces a MultiPolygon after buffering, when I was just expecting another single simple Polygon.
Why is this happening?
Can it be predicted?
The buffer value is 0.005
Input =
POLYGON ((0.7668779968807771 3.564681338871527, -1.0790828879893206 3.501372751894663, -1.079372080977487 3.501359499764618, -1.0833137671830821 3.5011789030229563,
-1.083633604054462 3.5011642513988437, -1.0948412046245983 3.501085737978757, -1.1035044526606603 3.5021750503003943, -1.1092779718019103 3.5043887609190154, -1.11193159005958 3.507638616178024, -1.1120870871650812 3.509266015629815, -1.1101726804479204 3.513752590267064,
-1.105102703636879 3.518902003217866, -1.0970792807081766 3.5245089636377847, -0.8470251304228252 3.6903184283228097, -0.8383719872228549 3.695350891964352, -0.8270067697589224 3.7004612010159508, -0.8133825733862969 3.7054456235822317, -0.7980425518207173
3.7101054464647314, -0.7815982633137657 3.7142548972300466, -0.7647052897552612 3.7177285503705133, -0.7480371006921206 3.720387922297167, -0.7322582042227791 3.722126992243426, -0.7179976551562821 3.722876428978485, -0.717673261034114 3.7228829968397594,
-0.713675455243893 3.7229639258667513, -0.7133821481068161 3.722969862463567, 0.409576015592515 3.7581984475865715, 0.4098997218464772 3.7582121751813182, 0.4138890938107309 3.7583813392173036, 0.4141817853445169 3.758393749282287, 0.4303753274802963 3.758309035355792,
0.4474831462576271 3.7574083282297925, 0.4648232069287013 3.7557275362550553, 0.4817042159942887 3.753333667303568, 0.4974531808940492 3.750322157376136, 0.5114422400961618 3.7468130658701964, 0.5231136939552675 3.7429462891905128, 0.5320022384374061 3.738875983520985,
0.8013745195980979 3.584413508988408, 0.8066688985032548 3.5798475649267116, 0.8086879717166704 3.5756280309670485, 0.8073512451608796 3.57192312661288, 0.8027120099053775 3.568880554709305, 0.7949552176198473 3.5666216129967294, 0.7843901071347398 3.5652363583527293,
0.7714378760649617 3.564780016508538, 0.7711481034342423 3.564773744187111, 0.7671984806856584 3.5646882725991955, 0.7668779968808073 3.564681338871528, 0.7668779968807771 3.564681338871527))
Output=
MULTIPOLYGON (((0.7670177667522091 3.559683192752515, -1.0788827511919128 3.4963766761038007, -1.0791431985620081 3.4963647412279233, -1.0830849216142129 3.4961841427979197,
-1.0834047956185886 3.496169489472618, -1.0835985780499513 3.496164374082448, -1.0948061786200876 3.4960858606623613, -1.0954649902182996 3.4961248014206974, -1.1041282382543616 3.4972141137423347, -1.1052945051628429 3.497506462501131, -1.111068024304093
3.4997201731197523, -1.1118462598986802 3.5000987846659353, -1.1125475498547859 3.500605923444823, -1.1131508835998414 3.501226395632486, -1.1158045018575111 3.5044762508914946, -1.116347370341116 3.5052932197285513, -1.116720294116688 3.5062004529559117,
-1.116908920925257 3.507163035003481, -1.117064418030758 3.5087904344552716, -1.1170745151972197 3.5096203623868756, -1.1169471823230535 3.5104405261897735, -1.116685928102913 3.511228326010087, -1.114771521385752 3.515714900647336, -1.1143260868590648 3.5165363314877713,
-1.1137355887084566 3.5172605362083527, -1.1086656118974152 3.522409949159155, -1.107966779707328 3.523000425873313, -1.0999433567786256 3.5286073862932317, -1.0998424669828828 3.5286760731409386, -0.8497883166975315 3.6944855378259636, -0.8495388174490363
3.6946406242385748, -0.8408856742490659 3.699673087880117, -0.8404224628749387 3.6999111057312946, -0.8290572454110062 3.7050214147828933, -0.8287246654020657 3.7051568196715987, -0.8151004690294402 3.7101412422378797, -0.8148358467970112 3.7102297636714967,
-0.7994958252314315 3.7148895865539964, -0.799265876091629 3.7149534850091532, -0.7828215875846775 3.7191029357744685, -0.7826053286054429 3.719152429210371, -0.7657123550469384 3.7226260823508377, -0.7654930648756366 3.7226661014193345, -0.748824875812496
3.7253254733459884, -0.7485848584795459 3.7253578278703463, -0.7328059620102044 3.727096897816605, -0.7325206078513746 3.727120101929353, -0.7182600587848776 3.7278695386644123, -0.7180988671555387 3.7278754044866473, -0.7177744730333706 3.7278819723479217,
-0.7137766513177277 3.7279629016973233, -0.7135111317744486 3.7279682758675468, 0.4093916967563248 3.7631951250579414, 0.4096878744178587 3.7632076852320524, 0.4136772657864812 3.7633768500908924, 0.4139699766054192 3.7633892609735997, 0.4142079416871592 3.7633936808663933,
0.4304014838229386 3.7633089669398982, 0.4306382076846225 3.7633021199733583, 0.4477460264619533 3.7624014128473586, 0.4479655410864408 3.7623850033476933, 0.4653056017575151 3.760704211372956, 0.4655252254187507 3.7606780079537554, 0.4824062344843381 3.758284139002268,
0.4826432991180261 3.758244687858067, 0.4983922640177866 3.7552331779306347, 0.4986697175516882 3.75517190361286, 0.5126587767538007 3.7516628121069204, 0.5130146993400074 3.751559366737866, 0.5246861531991132 3.7476925900581826, 0.52519544135618 3.7474923124811257,
0.5340839858383186 3.7434220068115978, 0.5344894300494842 3.743213480251221, 0.803861711210176 3.588751005718644, 0.804639966114085 3.5881999134902047, 0.8099343450192419 3.5836339694285084, 0.8106410650144498 3.582884321948164, 0.811179138816105 3.582005742936131,
0.8131982120295206 3.577786208976468, 0.81353479784346 3.5768561500560097, 0.8136817177338558 3.5758780323987334, 0.8136332224338748 3.574890131689376, 0.8133912096608308 3.5739311064429136, 0.81205448310504 3.570226202088745, 0.8115849902836264 3.569263163786896,
0.8109211065316004 3.5684222567504267, 0.8100933138398786 3.5677420909326147, 0.8054540785843765 3.56469951902904, 0.8048051077588819 3.564339746259739, 0.8041100385816038 3.564079980179059, 0.7963532462960736 3.561821038466483, 0.795605233904561 3.561664045162639,
0.7850401234194534 3.560278790518639, 0.7845661613091248 3.560239458821252, 0.7716139302393468 3.5597831169770604, 0.771546079046851 3.5597811874341736, 0.7712563064161316 3.5597749151127465, 0.7673066575760012 3.5596894429601305, 0.7670177667522091 3.559683192752515)),
((0.7670231773825333 3.559745201812444, 0.767023177382545 3.5597452018124445, 0.7670249921388167 3.559683500099206, 0.7670249921387865 3.5596835000992053, 0.7670231773825148 3.5597452018124436, 0.7670231773825333 3.559745201812444)))
Jim Kay
From: jts-dev-bounces@xxxxxxxxxxxxxxxx [mailto:jts-dev-bounces@xxxxxxxxxxxxxxxx]
On Behalf Of Martin Davis
Sent: 23 September 2016 17:36
To: JTS developer discussions
Subject: Re: [jts-dev] Struggling with polygon topology again. Overlapping inner polygons.
On Thu, Sep 22, 2016 at 2:45 PM, Phil Scadden <p.scadden@xxxxxxxxxx> wrote:
>1. For polygons which have "loops" in their shell, buffer(0) may FAIL because it keeps only one of the loops (and may choose the smaller one).
>2. For polygons with rings that touch but do not cross, buffer(0) should produce VALID output
That is excellent information. What about the more common case of internal rings that overlap?
Hole rings that overlap should also produce valid output, but perhaps not in the way you might expect. The entire area covered by the holes will be merged into a single hole (which makes topological sense, since the hole areas were exterior
to the polygon to begin with).
