47 lines
1.7 KiB
JavaScript
Executable File
47 lines
1.7 KiB
JavaScript
Executable File
import { featureCollection } from "@turf/helpers";
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import Graph from "./lib/Graph.js";
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import EdgeRing from "./lib/EdgeRing.js";
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/**
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* Polygonizes {@link LineString|(Multi)LineString(s)} into {@link Polygons}.
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*
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* Implementation of GEOSPolygonize function (`geos::operation::polygonize::Polygonizer`).
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*
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* Polygonizes a set of lines that represents edges in a planar graph. Edges must be correctly
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* noded, i.e., they must only meet at their endpoints.
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*
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* The implementation correctly handles:
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*
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* - Dangles: edges which have one or both ends which are not incident on another edge endpoint.
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* - Cut Edges (bridges): edges that are connected at both ends but which do not form part of a polygon.
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*
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* @name polygonize
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* @param {FeatureCollection|Geometry|Feature<LineString|MultiLineString>} geoJson Lines in order to polygonize
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* @returns {FeatureCollection<Polygon>} Polygons created
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* @throws {Error} if geoJson is invalid.
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*/
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export default function polygonize(geoJson) {
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var graph = Graph.fromGeoJson(geoJson);
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// 1. Remove dangle node
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graph.deleteDangles();
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// 2. Remove cut-edges (bridge edges)
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graph.deleteCutEdges();
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// 3. Get all holes and shells
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var holes = [], shells = [];
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graph
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.getEdgeRings()
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.filter(function (edgeRing) { return edgeRing.isValid(); })
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.forEach(function (edgeRing) {
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if (edgeRing.isHole())
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holes.push(edgeRing);
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else
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shells.push(edgeRing);
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});
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// 4. Assign Holes to Shells
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holes.forEach(function (hole) {
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if (EdgeRing.findEdgeRingContaining(hole, shells))
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shells.push(hole);
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});
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// 5. EdgeRings to Polygons
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return featureCollection(shells.map(function (shell) { return shell.toPolygon(); }));
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}
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