Add GeometryCollection dimension cache (#1103)

modules/core/src/main/java/org/locationtech/jts/geom/GeometryCollection.java

@@ -31,6 +31,7 @@ public class GeometryCollection extends Geometry {
    *  Internal representation of this <code>GeometryCollection</code>.
    */
   protected Geometry[] geometries;
+  private GeometryCollectionDimension geomCollDim;
 
   /** @deprecated Use GeometryFactory instead */
   public GeometryCollection(Geometry[] geometries, PrecisionModel precisionModel, int SRID) {
@@ -97,19 +98,26 @@ public boolean isEmpty() {
   }
 
   public int getDimension() {
+    /*
     int dimension = Dimension.FALSE;
     for (int i = 0; i < geometries.length; i++) {
       dimension = Math.max(dimension, geometries[i].getDimension());
     }
     return dimension;
+    //*/
+ //*
+    if (geomCollDim == null) {
+      geomCollDim = new GeometryCollectionDimension(this);
+    }
+    return geomCollDim.getDimension();
+    //*/
   }
 
   public boolean hasDimension(int dim) {
-    for (int i = 0; i < geometries.length; i++) {
-      if (geometries[i].hasDimension(dim))
-        return true;
+    if (geomCollDim == null) {
+      geomCollDim = new GeometryCollectionDimension(this);
     }
-    return false;
+    return geomCollDim.hasDimension(dim);
   }
 
   public int getBoundaryDimension() {

modules/core/src/main/java/org/locationtech/jts/geom/GeometryCollectionDimension.java

@@ -0,0 +1,63 @@
+/*
+ * Copyright (c) 2024 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.geom;
+
+import java.util.Iterator;
+
+/**
+ * Computes and caches dimension information for {@link GeometryCollection}s.
+ * Optimizes performance of dimension reporting for heterogeneous collections.
+ * 
+ * @author mdavis
+ */
+class GeometryCollectionDimension {
+  private int dimension = Dimension.FALSE;
+  private boolean hasP = false;
+  private boolean hasL = false;
+  private boolean hasA = false;
+
+  public GeometryCollectionDimension(GeometryCollection coll) {
+    init(coll);
+  }
+
+  private void init(GeometryCollection coll) {
+    Iterator geomi = new GeometryCollectionIterator(coll);
+    while (geomi.hasNext()) {
+      Geometry elem = (Geometry) geomi.next();
+      //-- empty elements still determine dimension, to match previous semantics
+      if (elem instanceof Point) {
+        hasP = true;
+        if (dimension < Dimension.P) dimension = Dimension.P;
+      }
+      if (elem instanceof LineString) {
+        hasL = true;
+        if (dimension < Dimension.L) dimension = Dimension.L;
+      }
+      if (elem instanceof Polygon) {
+        hasA = true;
+        if (dimension < Dimension.A) dimension = Dimension.A;
+      }
+    }
+  }
+
+  public boolean hasDimension(int dim) {
+    if (dim == Dimension.A && hasA) return true;
+    if (dim == Dimension.L && hasL) return true;
+    if (dim == Dimension.P && hasP) return true;
+    return false;
+  }
+
+  public int getDimension() {
+    return dimension;
+  }
+
+}

modules/core/src/test/java/test/jts/perf/coverage/CoverageUnionPerfTest.java

@@ -0,0 +1,80 @@
+/*
+ * Copyright (c) 2024 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 test.jts.perf.coverage;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.locationtech.jts.geom.Envelope;
+import org.locationtech.jts.geom.Geometry;
+import org.locationtech.jts.geom.GeometryFactory;
+import org.locationtech.jts.operation.overlayng.CoverageUnion;
+
+import test.jts.perf.PerformanceTestCase;
+import test.jts.perf.PerformanceTestRunner;
+
+/**
+ * Shows how linear performance of {@link GeometryCollection#getDimension()}
+ * affects performance.
+ * (See https://github.com/locationtech/jts/issues/1100)
+ * 
+ * @author mdavis
+ *
+ */
+public class CoverageUnionPerfTest  extends PerformanceTestCase
+{
+  public static void main(String[] args) {
+    PerformanceTestRunner.run(CoverageUnionPerfTest.class);  
+  }
+
+  private Geometry grid;
+
+  public CoverageUnionPerfTest(String name) {
+    super(name);
+    setRunSize(new int[] { 10_000, 20_000, 40_000, 100_000, 200_000, 400_000 });
+  }
+
+  public void startRun(int nCells)
+  {
+    grid = createGrid(100.0, nCells, new GeometryFactory());
+    System.out.println("\n-------  Running with cells = " + nCells);
+  }
+
+  private static Geometry createGrid(double size, int nCells, GeometryFactory geomFact) {
+
+    int nCellsOnSideY = (int) Math.sqrt(nCells);
+    int nCellsOnSideX = nCells / nCellsOnSideY;
+
+    double cellSizeX = size / nCellsOnSideX;
+    double cellSizeY = size / nCellsOnSideY;
+
+    List<Geometry> geoms = new ArrayList<Geometry>(); 
+
+    for (int i = 0; i < nCellsOnSideX; i++) {
+      for (int j = 0; j < nCellsOnSideY; j++) {
+        double x = 0 + i * cellSizeX;
+        double y = 0 + j * cellSizeY;
+        double x2 = 0 + (i + 1) * cellSizeX;
+        double y2 = 0 + (j + 1) * cellSizeY;
+
+        Envelope cellEnv = new Envelope(x, x2, y, y2);
+        geoms.add(geomFact.toGeometry(cellEnv));
+      }
+    }
+    return geomFact.createGeometryCollection(
+        GeometryFactory.toGeometryArray(geoms));
+  }
+
+  public void runUnion() {
+    CoverageUnion.union(grid);
+  }
+}