Add Densifer setValidated method (#595)

Signed-off-by: Martin Davis <mtnclimb@gmail.com>

modules/core/src/main/java/org/locationtech/jts/densify/Densifier.java

@@ -31,6 +31,10 @@
  * The coordinates created during densification respect the input geometry's
  * {@link PrecisionModel}.
  * <p>
+ * By default polygonal results are processed to ensure they are valid.
+ * This processing is costly, and it is very rare for results to be invalid.
+ * Validation processing can be disabled by calling the {@link #setValidate(boolean)} method.
+ * <p>
  * <b>Note:</b> At some future point this class will
  * offer a variety of densification strategies.
  * 
@@ -86,6 +90,11 @@ private static Coordinate[] densifyPoints(Coordinate[] pts,
 
 	private double distanceTolerance;
 
+	/**
+	 * Indicates whether areas should be topologically validated.
+	 */
+  private boolean isValidated = true;
+
 	/**
 	 * Creates a new densifier instance.
 	 * 
@@ -110,20 +119,31 @@ public void setDistanceTolerance(double distanceTolerance) {
 		this.distanceTolerance = distanceTolerance;
 	}
 
+	/**
+	 * Sets whether polygonal results are processed to ensure they are valid.
+	 * 
+	 * @param isValidated true if the results should be validated
+	 */
+	public void setValidate(boolean isValidated) {
+	  this.isValidated  = isValidated;
+	}
+
 	/**
 	 * Gets the densified geometry.
 	 * 
 	 * @return the densified geometry
 	 */
 	public Geometry getResultGeometry() {
-		return (new DensifyTransformer(distanceTolerance)).transform(inputGeom);
+		return (new DensifyTransformer(distanceTolerance, isValidated)).transform(inputGeom);
 	}
 
 	static class DensifyTransformer extends GeometryTransformer {
 	  double distanceTolerance;
+    private boolean isValidated;
 
-	  DensifyTransformer(double distanceTolerance) {
+	  DensifyTransformer(double distanceTolerance, boolean isValidated) {
 	    this.distanceTolerance = distanceTolerance;
+	    this.isValidated = isValidated;
     }
 
 		protected CoordinateSequence transformCoordinates(
@@ -165,6 +185,7 @@ protected Geometry transformMultiPolygon(MultiPolygon geom, Geometry parent) {
 		 * @return a valid area geometry
 		 */
 		private Geometry createValidArea(Geometry roughAreaGeom) {
+		  if (! isValidated) return roughAreaGeom;
 			return roughAreaGeom.buffer(0.0);
 		}
 	}

modules/core/src/test/java/org/locationtech/jts/densify/DensifierTest.java

@@ -0,0 +1,68 @@
+/*
+ * 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.jts.densify;
+
+import org.locationtech.jts.geom.Geometry;
+
+import junit.textui.TestRunner;
+import test.jts.GeometryTestCase;
+
+public class DensifierTest extends GeometryTestCase {
+  private static final double TOLERANCE = 1e-6;
+
+  public static void main(String args[]) {
+    TestRunner.run(DensifierTest.class);
+  }
+
+  public DensifierTest(String name) { super(name); }
+
+  public void testLine() {
+    checkDensify("LINESTRING (0 0, 30 40, 35 35)", 
+        10, "LINESTRING (0 0, 5 6.666666666666668, 10 13.333333333333336, 15 20, 20 26.66666666666667, 25 33.33333333333334, 30 40, 35 35)");
+  }
+
+  public void testBox() {
+    checkDensify("POLYGON ((10 30, 30 30, 30 10, 10 10, 10 30))", 
+        10, "POLYGON ((10 30, 16.666666666666668 30, 23.333333333333336 30, 30 30, 30 23.333333333333332, 30 16.666666666666664, 30 10, 23.333333333333332 10, 16.666666666666664 10, 10 10, 10 16.666666666666668, 10 23.333333333333336, 10 30))");
+  }
+
+  public void testBoxNoValidate() {
+    checkDensifyNoValidate("POLYGON ((10 30, 30 30, 30 10, 10 10, 10 30))", 
+        10, "POLYGON ((10 30, 16.666666666666668 30, 23.333333333333336 30, 30 30, 30 23.333333333333332, 30 16.666666666666664, 30 10, 23.333333333333332 10, 16.666666666666664 10, 10 10, 10 16.666666666666668, 10 23.333333333333336, 10 30))");
+  }
+
+  private void checkDensify(String wkt, double distanceTolerance, String wktExpected) {
+    Geometry geom = read(wkt);
+    Geometry expected = read(wktExpected);
+    Geometry actual = Densifier.densify(geom, distanceTolerance);
+    checkEqual(expected, actual, TOLERANCE);
+  }
+
+  /**
+   * Note: it's hard to construct a geometry which would actually be invalid when densified.
+   * This test just checks that the code path executes.
+   * 
+   * @param wkt
+   * @param distanceTolerance
+   * @param wktExpected
+   */
+  private void checkDensifyNoValidate(String wkt, double distanceTolerance, String wktExpected) {
+    Geometry geom = read(wkt);
+    Geometry expected = read(wktExpected);
+    Densifier den = new Densifier(geom);
+    den.setDistanceTolerance(distanceTolerance);
+    den.setValidate(false);
+    Geometry actual = den.getResultGeometry();
+    checkEqual(expected, actual, TOLERANCE);
+  }
+
+}