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fix(polygonize): deduplicate segments in planar graph #3045

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fix(polygonize): deduplicate segments in planar graph #3045

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cdf09f2
fix(polygonize): ignore duplicate segments in planar graph
Traksewt Mar 31, 2026
7bc825d
chore: add contributor to package.json
Traksewt Mar 31, 2026
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12 changes: 10 additions & 2 deletions packages/turf-polygonize/lib/Graph.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -44,6 +44,7 @@ function validateGeoJson(geoJson: AllGeoJSON) {
class Graph {
private nodes: { [id: string]: Node };
private edges: Edge[];
private edgeIds: { [id: string]: true };

/**
* Creates a graph from a GeoJSON.
Expand Down Expand Up @@ -102,15 +103,21 @@ class Graph {
* @param {Node} to - Node which ends the Edge
*/
addEdge(from: Node, to: Node) {
const edge = new Edge(from, to),
symetricEdge = edge.getSymetric();
const edgeId = `${from.id}->${to.id}`;
if (this.edgeIds[edgeId]) return;

const edge = new Edge(from, to);
const symetricEdge = edge.getSymetric();

this.edgeIds[`${edge.from.id}->${edge.to.id}`] = true;
this.edgeIds[`${symetricEdge.from.id}->${symetricEdge.to.id}`] = true;
this.edges.push(edge);
this.edges.push(symetricEdge);
}

constructor() {
this.edges = []; //< {Edge[]} dirEdges
this.edgeIds = {};

// The key is the `id` of the Node (ie: coordinates.join(','))
this.nodes = {};
Expand Down Expand Up @@ -348,6 +355,7 @@ class Graph {
removeEdge(edge: Edge) {
this.edges = this.edges.filter((e) => !e.isEqual(edge));
edge.deleteEdge();
delete this.edgeIds[`${edge.from.id}->${edge.to.id}`];
}
}

Expand Down
3 changes: 2 additions & 1 deletion packages/turf-polygonize/package.json
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,8 @@
"author": "Turf Authors",
"contributors": [
"Nicolas Cisco <@nickcis>",
"Denis Carriere <@DenisCarriere>"
"Denis Carriere <@DenisCarriere>",
"Kenny Sabir <@Traksewt>"
],
"license": "MIT",
"bugs": {
Expand Down
34 changes: 34 additions & 0 deletions packages/turf-polygonize/test.ts
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Expand Up @@ -81,6 +81,40 @@ test("turf-polygonize -- input mutation", (t) => {
t.end();
});

test("turf-polygonize -- duplicate segment", (t) => {
const lines = featureCollection([
lineString([
[0, 0],
[1, 0],
]),
lineString([
[1, 0],
[1, 1],
]),
lineString([
[1, 1],
[0, 1],
]),
lineString([
[0, 1],
[0, 0],
]),
// Duplicate boundary segment should not prevent polygonization.
lineString([
[0, 0],
[1, 0],
]),
]);

const polygonized = polygonize(lines);
t.equal(
polygonized.features.length,
1,
"returns one polygon for closed ring with duplicate edge"
);
t.end();
});

function colorize(feature, color = "#F00", width = 6) {
feature.properties["fill"] = color;
feature.properties["fill-opacity"] = 0.3;
Expand Down