Add PolygonHull class (#861)

Signed-off-by: Martin Davis <[email protected]>

modules/app/src/main/java/org/locationtech/jtstest/function/HullFunctions.java

@@ -0,0 +1,83 @@
+/*
+ * Copyright (c) 2016 Vivid Solutions.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
+ * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ */
+package org.locationtech.jtstest.function;
+
+import org.locationtech.jts.algorithm.hull.ConcaveHull;
+import org.locationtech.jts.algorithm.hull.PolygonHull;
+import org.locationtech.jts.geom.Geometry;
+import org.locationtech.jtstest.geomfunction.Metadata;
+
+public class HullFunctions {
+  public static Geometry convexHull(Geometry g) {      return g.convexHull();  }
+
+  public static Geometry concaveHullByLen(Geometry geom, 
+      @Metadata(title="Length")
+      double maxLen) {
+    return ConcaveHull.concaveHullByLength(geom, maxLen);
+  }
+
+  public static Geometry concaveHullWithHolesByLen(Geometry geom, 
+      @Metadata(title="Length")
+      double maxLen) {
+    return ConcaveHull.concaveHullByLength(geom, maxLen, true);
+  }
+
+  public static Geometry concaveHullByLenRatio(Geometry geom, 
+      @Metadata(title="Length Ratio")
+      double maxLen) {
+    return ConcaveHull.concaveHullByLengthRatio(geom, maxLen);
+  }
+
+  public static Geometry concaveHullWithHolesByLenRatio(Geometry geom, 
+      @Metadata(title="Length Ratio")
+      double maxLen) {
+    return ConcaveHull.concaveHullByLengthRatio(geom, maxLen, true);
+  }
+
+  public static double concaveHullLenGuess(Geometry geom) {
+    return ConcaveHull.uniformGridEdgeLength(geom);
+  }
+
+  /**
+   * A concaveness measure defined in terms of the perimeter length
+   * relative to the convex hull perimeter.
+   * <pre>
+   * C = ( P(geom) - P(CH) ) / P(CH)
+   * </pre>
+   * Concaveness values are >= 0.  
+   * A convex polygon has C = 0. 
+   * A higher concaveness indicates a more concave polygon.
+   * <p>
+   * Originally defined by Park & Oh, 2012.
+   * 
+   * @param geom a polygonal geometry
+   * @return the concaveness measure of the geometry
+   */
+  public static double concaveness(Geometry geom) {
+    double convexLen = geom.convexHull().getLength();
+    return (geom.getLength() - convexLen) / convexLen;
+  }
+
+  public static Geometry polygonHull(Geometry geom, 
+      @Metadata(title="Vertex Frac")
+      double vertexFrac) {
+    return PolygonHull.hull(geom, vertexFrac);
+  }
+
+  public static Geometry polygonHullByArea(Geometry geom, 
+      @Metadata(title="Area Delta Ratio")
+      double areaFrac) {
+    return PolygonHull.hullByAreaDelta(geom, areaFrac);
+  }
+
+
+}

modules/app/src/main/java/org/locationtech/jtstest/geomfunction/GeometryFunctionRegistry.java

@@ -37,6 +37,7 @@
 import org.locationtech.jtstest.function.DoubleKeyMap;
 import org.locationtech.jtstest.function.EditFunctions;
 import org.locationtech.jtstest.function.GeometryFunctions;
+import org.locationtech.jtstest.function.HullFunctions;
 import org.locationtech.jtstest.function.JTSFunctions;
 import org.locationtech.jtstest.function.LineHandlingFunctions;
 import org.locationtech.jtstest.function.LineSegmentFunctions;
@@ -91,6 +92,7 @@ public static GeometryFunctionRegistry createTestBuilderRegistry()
     funcRegistry.add(ConstructionFunctions.class);
     funcRegistry.add(ConversionFunctions.class);
     funcRegistry.add(EditFunctions.class);
+    funcRegistry.add(HullFunctions.class);
     funcRegistry.add(LinearReferencingFunctions.class);
     funcRegistry.add(LineHandlingFunctions.class);
     funcRegistry.add(NodingFunctions.class);

modules/core/src/main/java/org/locationtech/jts/algorithm/hull/LinkedRing.java

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2021 Martin Davis.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * and Eclipse Distribution License v. 1.0 which accompanies this distribution.
+ * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *
+ * http://www.eclipse.org/org/documents/edl-v10.php.
+ */
+package org.locationtech.jts.algorithm.hull;
+
+import org.locationtech.jts.geom.Coordinate;
+import org.locationtech.jts.geom.CoordinateList;
+
+class LinkedRing {
+
+  private static final int NO_COORD_INDEX = -1;
+
+  private final Coordinate[] coord;
+  private int[] next = null;
+  private int[] prev = null;
+  private int size;
+
+  public LinkedRing(Coordinate[] pts) {
+    coord = pts;
+    size = pts.length - 1;
+    next = createNextLinks(size);
+    prev = createPrevLinks(size);
+  }
+
+  private static int[] createNextLinks(int size) {
+    int[] next = new int[size];
+    for (int i = 0; i < size; i++) {
+      next[i] = i + 1;
+    }
+    next[size - 1] = 0;
+    return next;
+  }
+
+  private static int[] createPrevLinks(int size) {
+    int[] prev = new int[size];
+    for (int i = 0; i < size; i++) {
+      prev[i] = i - 1;
+    }
+    prev[0] = size - 1;
+    return prev;
+  }
+
+  public int size() {
+    return size;
+  }
+
+  public int next(int i) {
+    return next[i];
+  }
+
+  public int prev(int i) {
+    return prev[i];
+  }
+
+  public Coordinate getCoordinate(int index) {
+    return coord[index];
+  }
+
+  public Coordinate prevCoordinate(int index) {
+    return coord[prev(index)];
+  }
+
+  public Coordinate nextCoordinate(int index) {
+    return coord[next(index)];
+  }  
+
+  public boolean hasCoordinate(int index) {
+    return index >= 0 && index < prev.length 
+        && prev[index] != NO_COORD_INDEX;
+  }
+
+  public void remove(int index) {
+    int iprev = prev[index];
+    int inext = next[index];
+    next[iprev] = inext;
+    prev[inext] = iprev;
+    prev[index] = NO_COORD_INDEX;
+    next[index] = NO_COORD_INDEX;
+    size--;
+  }
+
+  public Coordinate[] getCoordinates() {
+    CoordinateList coords = new CoordinateList();
+    for (int i = 0; i < coord.length - 1; i++) {
+      if (prev[i] != NO_COORD_INDEX) {
+        coords.add(coord[i].copy(), false);
+      }
+    }
+    coords.closeRing();
+    return coords.toCoordinateArray();
+  }
+}