Fix Angle#interiorAngle method (#721) (#723)

Signed-off-by: grimsa <gediminas.rimsa@gmail.com>
locationtech · May 21, 2021 · 480301f · 480301f
1 parent e570d57
commit 480301f
Show file tree

Hide file tree

Showing 3 changed files with 59 additions and 11 deletions.
diff --git a/doc/JTS_Version_History.md b/doc/JTS_Version_History.md
@@ -38,6 +38,7 @@ Distributions for older JTS versions can be obtained at the
 * Fix `HalfEdge.prev()` method (#703)
 * Fix `BufferOp` to remove invalid elements caused by inverted ring curves (#706) 
 * Fix `IsSimpleOp` duplicate lines bug (#716)
+* Fix `Angle.interiorAngle` to produce interior angle correctly (#721)
 
 <!-- ================================================================ -->
 

diff --git a/modules/core/src/main/java/org/locationtech/jts/algorithm/Angle.java b/modules/core/src/main/java/org/locationtech/jts/algorithm/Angle.java
@@ -198,7 +198,7 @@ public static double interiorAngle(Coordinate p0, Coordinate p1, Coordinate p2)
   {
     double anglePrev = Angle.angle(p1, p0);
     double angleNext = Angle.angle(p1, p2);
-    return Math.abs(angleNext - anglePrev);
+    return normalizePositive(angleNext - anglePrev);
   }
 
   /**

diff --git a/modules/core/src/test/java/org/locationtech/jts/algorithm/AngleTest.java b/modules/core/src/test/java/org/locationtech/jts/algorithm/AngleTest.java
@@ -16,8 +16,15 @@
 
 import junit.framework.TestCase;
 import junit.textui.TestRunner;
+import org.locationtech.jts.geom.CoordinateSequenceFactory;
+import org.locationtech.jts.geom.CoordinateSequences;
+import org.locationtech.jts.geom.CoordinateXY;
+import org.locationtech.jts.geom.Geometry;
+import org.locationtech.jts.geom.GeometryFactory;
+import org.locationtech.jts.geom.Polygon;
+import org.locationtech.jts.shape.random.RandomPointsBuilder;
 
-
+import java.util.Arrays;
 
 /**
  * @version 1.7
@@ -32,7 +39,7 @@ public static void main(String args[]) {
 
   public AngleTest(String name) { super(name); }
 
-  public void testAngle() throws Exception
+  public void testAngle()
   {
 		assertEquals(Angle.angle(new Coordinate(10,0)), 0.0, TOLERANCE);
 		assertEquals(Angle.angle(new Coordinate(10,10)), Math.PI/4, TOLERANCE);
@@ -43,7 +50,7 @@ public void testAngle() throws Exception
 		assertEquals(Angle.angle(new Coordinate(-10,-10)), -0.75*Math.PI, TOLERANCE);
   }
 
-  public void testIsAcute() throws Exception
+  public void testIsAcute()
   {
   	assertEquals(Angle.isAcute(new Coordinate(10,0), new Coordinate(0,0), new Coordinate(5,10)), true);
   	assertEquals(Angle.isAcute(new Coordinate(10,0), new Coordinate(0,0), new Coordinate(5,-10)), true);
@@ -52,11 +59,9 @@ public void testIsAcute() throws Exception
 
   	assertEquals(Angle.isAcute(new Coordinate(10,0), new Coordinate(0,0), new Coordinate(-5,10)), false);
   	assertEquals(Angle.isAcute(new Coordinate(10,0), new Coordinate(0,0), new Coordinate(-5,-10)), false);
-
-
   }
 
-  public void testNormalizePositive() throws Exception
+  public void testNormalizePositive()
   {
 		assertEquals(Angle.normalizePositive(0.0), 0.0, TOLERANCE);
 
@@ -75,10 +80,9 @@ public void testNormalizePositive() throws Exception
 		assertEquals(Angle.normalizePositive(2.5*Math.PI), 0.5*Math.PI, TOLERANCE);
 		assertEquals(Angle.normalizePositive(3*Math.PI), Math.PI, TOLERANCE);	
 		assertEquals(Angle.normalizePositive(4 * Math.PI), 0.0, TOLERANCE);
-
   }
 
-  public void testNormalize() throws Exception
+  public void testNormalize()
   {
 		assertEquals(Angle.normalize(0.0), 0.0, TOLERANCE);
 
@@ -97,9 +101,52 @@ public void testNormalize() throws Exception
 		assertEquals(Angle.normalize(2.5*Math.PI), 0.5*Math.PI, TOLERANCE);
 		assertEquals(Angle.normalize(3*Math.PI), Math.PI, TOLERANCE);	
 		assertEquals(Angle.normalize(4 * Math.PI), 0.0, TOLERANCE);
-
-
   }
 
+  public void testInteriorAngle() {
+		Coordinate p1 = new CoordinateXY(1, 2);
+		Coordinate p2 = new CoordinateXY(3, 2);
+		Coordinate p3 = new CoordinateXY(2, 1);
+
+		// Tests all interior angles of a triangle "POLYGON ((1 2, 3 2, 2 1, 1 2))"
+		assertEquals(45, Math.toDegrees(Angle.interiorAngle(p1, p2, p3)), 0.01);
+		assertEquals(90, Math.toDegrees(Angle.interiorAngle(p2, p3, p1)), 0.01);
+		assertEquals(45, Math.toDegrees(Angle.interiorAngle(p3, p1, p2)), 0.01);
+		// Tests interior angles greater than 180 degrees
+		assertEquals(315, Math.toDegrees(Angle.interiorAngle(p3, p2, p1)), 0.01);
+		assertEquals(270, Math.toDegrees(Angle.interiorAngle(p1, p3, p2)), 0.01);
+		assertEquals(315, Math.toDegrees(Angle.interiorAngle(p2, p1, p3)), 0.01);
+  }
 
+  /**
+   * Tests interior angle calculation using a number of random triangles
+   */
+  public void testInteriorAngle_randomTriangles() {
+		GeometryFactory geometryFactory = new GeometryFactory();
+		CoordinateSequenceFactory coordinateSequenceFactory = geometryFactory.getCoordinateSequenceFactory();
+		for (int i = 0; i < 100; i++){
+			RandomPointsBuilder builder = new RandomPointsBuilder();
+			builder.setNumPoints(3);
+			Geometry threeRandomPoints = builder.getGeometry();
+			Polygon triangle = geometryFactory.createPolygon(
+					CoordinateSequences.ensureValidRing(
+							coordinateSequenceFactory,
+							coordinateSequenceFactory.create(threeRandomPoints.getCoordinates())
+					)
+			);
+			// Triangle coordinates in clockwise order
+			Coordinate[] c = Orientation.isCCW(triangle.getCoordinates())
+					? triangle.reverse().getCoordinates()
+					: triangle.getCoordinates();
+			double sumOfInteriorAngles = Angle.interiorAngle(c[0], c[1], c[2])
+					+ Angle.interiorAngle(c[1], c[2], c[0])
+					+ Angle.interiorAngle(c[2], c[0], c[1]);
+			assertEquals(
+					i + ": The sum of the angles of a triangle is not equal to two right angles for points: " + Arrays.toString(c),
+					Math.PI,
+					sumOfInteriorAngles,
+					0.01
+			);
+		}
+  }
 }