Deconstruct polygon

[mofada]

Please provide the following when reporting an issue:

• "@turf/turf": "^6.5.0"
• GeoJSON data as a gist file or geojson.io (filename extension must be .geojson).
• Snippet of source code or for complex examples use jsfiddle.

how can i deconstruct polygon

I want to disassemble the polygon and disassemble the complete polygon below into polygons with multiple shaded parts. Is there any good way?
This means removing the parts where they overlap

example one

the code show with svg

<path stroke-linejoin="round" stroke-linecap="round" fill-rule="evenodd" stroke="#394381" stroke-width="5" stroke-dasharray="none" fill="#394381" stroke-opacity="1" fill-opacity="0.15" style="cursor: pointer; user-select: none;" d="M 455 350 L 447 472 631 469 632 457 607 421 603 399 531 402 529 477 535 505 536 572 575 558 612 553 789 549 825 544 825 494 819 440 797 370 764 377 738 375 755 499 755 535 745 581 721 588 622 594 622 562 616 530 617 517 624 513 673 504 724 503 911 480 903 423 891 416 791 415 735 422 695 419 695 376 688 316 586 316 582 367 482 373 479 427 398 423 395 356 455 350"></path>

geojson

{"type":"Feature","properties":{},"geometry":{"type":"Polygon","coordinates":[[[120.19970162302431,30.257965153582777],[120.19941416526112,30.254159311796954],[120.20602569381455,30.254252899856724],[120.20606162603495,30.254627251195146],[120.20516332052497,30.25575029656396],[120.20501959164338,30.256436595682302],[120.20243247177464,30.256343009724105],[120.20236060733384,30.25400333149719],[120.20257620065624,30.253129837195207],[120.20261213287664,30.251039658268134],[120.2040134894722,30.25147641578633],[120.20534298162697,30.251632400138938],[120.21170298463761,30.2517571874409],[120.21299654457198,30.251913171343205],[120.21299654457198,30.253472996606657],[120.21278095124958,30.25515757979106],[120.2119904424008,30.25734125530119],[120.21080467912763,30.25712288995689],[120.20987044139726,30.257185280105304],[120.21048128914404,30.253317015206104],[120.21048128914404,30.252193941736916],[120.21012196694005,30.25075888454217],[120.20925959365047,30.25054050441716],[120.20570230383096,30.250353321062605],[120.20570230383096,30.251351628124123],[120.20548671050857,30.252349924938734],[120.20552264272897,30.252755480092652],[120.20577416827176,30.252880265953618],[120.20753484707132,30.253161033555376],[120.20936739031167,30.253192229905533],[120.2160867155263,30.253909743197248],[120.21579925776311,30.255687905494828],[120.21536807111832,30.255906274061633],[120.21177484907841,30.25593746953114],[120.20976264473606,30.255719101034405],[120.2083253559201,30.255812687593053],[120.2083253559201,30.257154085036102],[120.2080738303773,30.25902577147406],[120.2044087438966,30.25902577147406],[120.204265015015,30.257434840298636],[120.20067179297509,30.257247670213683],[120.20056399631389,30.255563123236495],[120.19765348646156,30.255687905494828],[120.19754568980036,30.257777984518633],[120.19970162302431,30.257965153582777]]]}}

example two

the code show with svg

<path stroke-linejoin="round" stroke-linecap="round" fill-rule="evenodd" stroke="#394381" stroke-width="5" stroke-dasharray="none" fill="#394381" stroke-opacity="1" fill-opacity="0.15" style="cursor: pointer; user-select: none;" d="M 560 70 L 555 79 552 106 550 201 564 212 733 209 810 201 978 202 982 192 977 160 958 119 895 110 892 129 901 190 905 304 882 314 830 315 808 302 800 280 782 143 767 126 747 124 737 130 731 152 723 256 706 289 676 292 664 278 643 236 638 187 609 123 605 100 574 86 560 70"></path>

the code of geojson

{"type":"Feature","properties":{},"geometry":{"type":"Polygon","coordinates":[[[120.18832458374015,30.26042000341602],[120.18814492263816,30.260139256773105],[120.18803712597696,30.259297011980273],[120.18796526153616,30.25633350008231],[120.18846831262175,30.255990350764787],[120.1945408578692,30.256083937062385],[120.19730763883993,30.25633350008231],[120.20334425186698,30.25630230473984],[120.20348798074858,30.256614257714126],[120.20330831964658,30.257612500506582],[120.202625607459,30.25889148410748],[120.20036187757385,30.259172234353407],[120.20025408091266,30.258579538439],[120.20057747089625,30.256676648188886],[120.20072119977785,30.253120327239188],[120.19989475870867,30.252808363056616],[120.19802628324791,30.25277716658332],[120.19723577439913,30.253182719955618],[120.19694831663594,30.253869037194452],[120.19630153666876,30.258142812821777],[120.19576255336277,30.258673122244634],[120.19504390895479,30.25873551139834],[120.1946845867508,30.25854834381711],[120.1944689934284,30.25786205960343],[120.19418153566521,30.254617741385548],[120.19357068791842,30.253588271636715],[120.19249272130645,30.25349468293734],[120.19206153466166,30.253931429430533],[120.19130695803328,30.255241657141553],[120.19112729693128,30.256770233825982],[120.19008526253971,30.258766705960184],[120.18994153365811,30.25948417812031],[120.18882763482574,30.25992089771259],[120.18832458374015,30.26042000341602]]]}}

[smallsaucepan]

Hi @mofada. Have you taken a look at turf-unkink-polygon?

[mofada]

It's not working, this is my polygon show in map.

{"type":"Feature","properties":{},"geometry":{"type":"Polygon","coordinates":[[[120.75070606120724,30.754885079659967],[120.74919690795048,30.754823011202177],[120.74923284017088,30.754760942703975],[120.74926877239128,30.754667839880895],[120.74934063683207,30.75463680558633],[120.74937656905247,30.75451266830705],[120.74941250127287,30.754419565241516],[120.74944843349327,30.754326462085047],[120.74948436571367,30.75426439326356],[120.75106538341123,30.754171289955558],[120.75113724785203,30.754109221033048],[120.75113724785203,30.754078186556637],[120.75113724785203,30.754078186556637],[120.75113724785203,30.754078186556637],[120.75113724785203,30.754047152070125],[120.75117318007243,30.754016117573507],[120.75120911229283,30.75395404854997],[120.75120911229283,30.75392301402305],[120.75120911229283,30.75389197948602],[120.75124504451323,30.753829910381654],[120.75131690895402,30.75373680664935],[120.75135284117442,30.75367473744397],[120.75138877339482,30.75355059891197],[120.75142470561522,30.7534574949069],[120.75146063783562,30.75333335609202],[120.75149657005602,30.753209217115522],[120.75156843449682,30.75311611277707],[120.75160436671722,30.753023008347693],[120.75164029893762,30.752991973517695],[120.75167623115802,30.75289886896709],[120.75167623115802,30.752836799216176],[120.75171216337841,30.752774729424853],[120.75174809559881,30.7526816246621],[120.75181996003961,30.752650589720975],[120.75185589226001,30.752526449855466],[120.75192775670081,30.75240230982832],[120.75199962114161,30.752278169639535],[120.75199962114161,30.752154029289116],[120.7520714855824,30.752029888777052],[120.7521074178028,30.75190574810338],[120.7521433500232,30.751781607268043],[120.7521792822436,30.751719536789775],[120.752215214464,30.751657466271087],[120.752215214464,30.751595395711995],[120.7522511466844,30.7515333251125],[120.7522870789048,30.7515022897976],[120.7523230111252,30.751409183792273],[120.7523589433456,30.751378148436967],[120.7523589433456,30.751347113071546],[120.7523589433456,30.75128504231041],[120.7524308077864,30.751191936092948],[120.7524667400068,30.751129865230794],[120.7525386044476,30.751036758861808],[120.75257453666799,30.75094365240189],[120.75264640110879,30.750912616895047],[120.75271826554959,30.750850545851055],[120.75286199443119,30.750726403641853],[120.75293385887198,30.750664332476646],[120.75307758775358,30.750602261271034],[120.75314945219438,30.75057122565306],[120.75322131663518,30.750540190025],[120.75332911329637,30.75050915438683],[120.75340097773717,30.75047811873857],[120.75347284217797,30.75047811873857],[120.75358063883917,30.750447083080193],[120.75368843550037,30.750416047411722],[120.75383216438196,30.750416047411722],[120.75393996104316,30.750385011733147],[120.75415555436555,30.750385011733147],[120.75437114768795,30.750385011733147],[120.75458674101034,30.750416047411722],[120.75473046989194,30.750416047411722],[120.75491013099393,30.750447083080193],[120.75501792765513,30.75047811873857],[120.75519758875713,30.75047811873857],[120.75530538541832,30.75050915438683],[120.75548504652032,30.750540190025],[120.75566470762232,30.750602261271034],[120.75584436872431,30.750633296878885],[120.7560599620467,30.750726403641853],[120.7562396231487,30.750757439209313],[120.7563833520303,30.750819510313917],[120.7565270809119,30.75088158137811],[120.75667080979349,30.75097468789863],[120.75674267423429,30.751005723385266],[120.75681453867509,30.75106779432823],[120.75688640311589,30.751160900666928],[120.75695826755668,30.751191936092948],[120.75703013199748,30.75125400691469],[120.75706606421788,30.751316077696032],[120.75710199643828,30.751378148436967],[120.75710199643828,30.751409183792273],[120.75710199643828,30.751409183792273],[120.75713792865868,30.751440219137482],[120.75713792865868,30.751471254472587],[120.75717386087908,30.751471254472587],[120.75717386087908,30.7515022897976],[120.75717386087908,30.7515333251125],[120.75717386087908,30.7515333251125],[120.75717386087908,30.751564360417298],[120.75717386087908,30.751595395711995],[120.75713792865868,30.751626430996595],[120.75710199643828,30.75168850153548],[120.75710199643828,30.75175057203396],[120.75710199643828,30.751812642492034],[120.75703013199748,30.75190574810338],[120.75699419977708,30.751936783286947],[120.75695826755668,30.75199885362379],[120.75692233533628,30.752060923920226],[120.75688640311589,30.752091959053296],[120.75688640311589,30.75212299417626],[120.75681453867509,30.752154029289116],[120.75674267423429,30.752185064391877],[120.75663487757309,30.75224713456708],[120.7564552164711,30.752278169639535],[120.7563474198099,30.752278169639535],[120.7562396231487,30.752278169639535],[120.7561318264875,30.752278169639535],[120.7560240298263,30.752278169639535],[120.75595216538551,30.752278169639535],[120.75588030094471,30.752278169639535],[120.75573657206311,30.75221609948453],[120.75566470762232,30.752185064391877],[120.75555691096112,30.752154029289116],[120.75544911429992,30.752091959053296],[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error code

Uncaught Error: The input polygon may not have duplicate vertices (except for the first and last vertex of each ring)
    at simplepolygon (index.js:232:1)
    at eval (index.js:783:1)
    at eval (index.js:738:1)
    at geomEach (index.js:590:1)
    at flattenEach (index.js:729:1)
    at Module.unkinkPolygon (index.js:781:1)
    at endDraw (map-circle-util.js:117:1)
    at Pa.mouseUp (map-circle-util.js:41:1)
    at A.lang.Ja.dispatchEvent (getscript?v=3.0&ak=EFnLH6IGNwQRtyjQ4wIGXePI6w9HwEE5&services=&t=20231026190002:1:8793)
    at HTMLDocument.eval (eval at O_ (getscript?v=3.0&ak=EFnLH6IGNwQRtyjQ4wIGXePI6w9HwEE5&services=&t=20231026190002:1:81897), <anonymous>:1:5831)

[smallsaucepan]

The error message suggests there are duplicated points in your polygon. A quick scan of the geojson you provided shows at least one:

[
  120.75113724785203,
  30.754078186556637
],
[
  120.75113724785203,
  30.754078186556637
],

Perhaps try removing any duplicates (except for the first and last vertex as the error suggests) and see if you can get any further.

[mofada]

Yes, you're right. I am attempting to simplify the polygon to obtain a multipolygon. I will verify the disassembled polygon later.

[mofada]

Thank you for your answer. Now I can get multiple disassembled polygons, but a new problem has arisen. I don't know which ones should be removed or which ones should be kept. Or should I use turf.mask next?

复杂的

before

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unkinkPolygon after

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[mofada]

Can someone help me take a look? Please

[twelch]

If your polygon is self crossing as it looks, maybe try to call the buffer function on the polygon with a value of zero and see if it breaks it into pieces.

A function like https://github.com/rowanwins/sweepline-intersections can tell you exactly where the crossings occur and maybe you can figure out how to write an algorithm to break it up.

Since self crossing polygon is invalid, your options will be limited for turf functions designed to work with them.

You may find a "fix geometry" function in software like qgis will do what you want.

[mofada]

@twelch @smallsaucepan Thank you for your help, I have solved my problem.

I try to generate random points within the split polygon, and then determine whether these points are within the original polygon. If one is within the initial polygon, then it is the outer ring, otherwise it is the inner ring and should be cut off.

Then determine whether there is an intersection between the outer ring and the inner ring. If there is an intersection, use mask to process it. In the end, all outer rings are the final result.

This may not be the optimal solution, but it is the closest to the result I can think of.

Now it's just that the particularly complex polygons are not very accurate. I'll try to optimize them again.

[mofada]

I adjusted my thinking and no longer differentiate between inner and outer rings, because it is easy to misjudge the inner and outer rings when the graph resembles a nested ring.

The current idea is to first disassemble the polygon and obtain multiple split polygons. Loop through the polygon array, compare it with the current polygon, and find the intersection part, and then mask the intersection part. Finally, you will get a complete incomplete Nested tiled polygon array, then generate random points on the polygon array, determine whether the random points are in the original shape, and obtain the final result

[mofada]

The first picture is the original graph, the second picture is the final result.

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