Add optional pre triangulation for polygons when creating MLT #383
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,23 @@ | ||
| package com.mlt.converter.triangulation; | ||
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| import java.util.ArrayList; | ||
| import java.util.List; | ||
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| public class TriangulatedPolygon { | ||
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There was a problem hiding this comment. If I'm reading build.gradle correctly, it looks like we're compiling against java 17. If that's right could this class just be |
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| private final int numTrianglesPerPolygon; | ||
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| private final ArrayList<Integer> indexBuffer; | ||
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| TriangulatedPolygon(ArrayList<Integer> indexBuffer, int numTriangles) { | ||
| this.numTrianglesPerPolygon = numTriangles; | ||
| this.indexBuffer = indexBuffer; | ||
| } | ||
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| public Integer getNumTrianglesPerPolygon() { | ||
| return numTrianglesPerPolygon; | ||
| } | ||
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| public List<Integer> getIndexBuffer() { | ||
| return indexBuffer; | ||
| } | ||
| } | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,76 @@ | ||
| package com.mlt.converter.triangulation; | ||
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| import earcut4j.Earcut; | ||
| import java.util.ArrayList; | ||
| import java.util.List; | ||
| import org.apache.commons.lang3.ArrayUtils; | ||
| import org.locationtech.jts.geom.Coordinate; | ||
| import org.locationtech.jts.geom.MultiPolygon; | ||
| import org.locationtech.jts.geom.Polygon; | ||
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| public class TriangulationUtils { | ||
| private TriangulationUtils() {} | ||
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| public static TriangulatedPolygon triangulatePolygon(Polygon polygon) { | ||
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There was a problem hiding this comment. A |
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| var convertedCoordinates = convertCoordinates(polygon.getCoordinates()); | ||
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| List<Integer> triangles = Earcut.earcut(convertedCoordinates, null, 2); | ||
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| ArrayList<Integer> indexBuffer = new ArrayList<>(triangles); | ||
| var numTriangles = triangles.size() / 3; | ||
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| return new TriangulatedPolygon(indexBuffer, numTriangles); | ||
| } | ||
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| public static TriangulatedPolygon triangulatePolygonWithHoles(MultiPolygon multiPolygon) { | ||
| var holeIndex = 0; | ||
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| ArrayList<Double> multiPolygonCoordinates = new ArrayList<>(); | ||
| ArrayList<Integer> holeIndices = new ArrayList<>(); | ||
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| for (int i = 0; i < multiPolygon.getNumGeometries(); i++) { | ||
| // assertion: first polygon defines the outer linear ring and the other polygons define its | ||
| // holes! | ||
| if (i == 0) { | ||
| holeIndex = multiPolygon.getGeometryN(i).getCoordinates().length; | ||
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There was a problem hiding this comment. Each call to getCoordinates may be transforming a packed double[] CoordinateSequence to a |
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| holeIndices.add(holeIndex); | ||
| } else if (i != multiPolygon.getNumGeometries() - 1) { | ||
| holeIndex += multiPolygon.getGeometryN(i).getCoordinates().length; | ||
| holeIndices.add(holeIndex); | ||
| } | ||
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| var coordinates = multiPolygon.getGeometryN(i).getCoordinates(); | ||
| for (Coordinate coordinate : coordinates) { | ||
| multiPolygonCoordinates.add(coordinate.x); | ||
| multiPolygonCoordinates.add(coordinate.y); | ||
| if (!Double.isNaN(coordinate.z)) { | ||
| multiPolygonCoordinates.add(coordinate.z); | ||
| } | ||
| } | ||
| } | ||
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| var doubleArray = ArrayUtils.toPrimitive(multiPolygonCoordinates.toArray(new Double[0])); | ||
| List<Integer> triangleVertices = | ||
| Earcut.earcut(doubleArray, holeIndices.stream().mapToInt(Integer::intValue).toArray(), 2); | ||
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| ArrayList<Integer> indexBuffer = new ArrayList<>(triangleVertices); | ||
| var numTriangles = triangleVertices.size() / 3; | ||
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| return new TriangulatedPolygon(indexBuffer, numTriangles); | ||
| } | ||
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| private static double[] convertCoordinates(Coordinate[] coordinates) { | ||
| ArrayList<Double> convertedCoordinates = new ArrayList<>(); | ||
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| for (Coordinate coordinate : coordinates) { | ||
| convertedCoordinates.add(coordinate.x); | ||
| convertedCoordinates.add(coordinate.y); | ||
| if (!Double.isNaN(coordinate.z)) { | ||
| convertedCoordinates.add(coordinate.z); | ||
| } | ||
| } | ||
| Double[] array = convertedCoordinates.toArray(new Double[0]); | ||
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| return ArrayUtils.toPrimitive(array); | ||
| } | ||
| } | ||
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We already depend on JTS, which has a few built-in polygon triangulation utilities: https://github.com/locationtech/jts/tree/master/modules/core/src/main/java/org/locationtech/jts/triangulate/polygon - and I think
PolygonEarClipperis similar to earcut. Do you have any quality/performance comparison of those vs. earcut4j? If earcut4j performs better then adding a new dependency seems fine, but if not I'd default to the dependencies we already have.