Regularize internal names, add Triangle unit test

Author: dr-jts

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

@@ -113,13 +113,13 @@ public static HCoordinate perpendicularBisector(Coordinate a, Coordinate b)
    * @return the circumradius of the triangle
    */
   public static double circumradius(Coordinate a, Coordinate b, Coordinate c) {
-    double A = a.distance(b);
-    double B = b.distance(c);
-    double C = c.distance(a);
+    double lenAB = a.distance(b);
+    double lenBC = b.distance(c);
+    double lenCA = c.distance(a);
     double area = area(a, b, c);
     if (area == 0.0)
       return Double.POSITIVE_INFINITY;
-    return (A * B * C) / (4 * area);
+    return (lenAB * lenBC * lenCA) / (4 * area);
   }
 
   /**
@@ -262,7 +262,7 @@ private static double det(double m00, double m01, double m10, double m11)
    * the point at which the bisectors of the triangle's angles meet. It is the
    * centre of the triangle's <i>incircle</i>, which is the unique circle that
    * is tangent to each of the triangle's three sides
-   * (and hence the maximum inscribed circle).
+   * (and hence the Maximum Inscribed Circle).
    * <p>
    * The incentre always lies within the triangle.
    * 
@@ -276,14 +276,13 @@ private static double det(double m00, double m01, double m10, double m11)
    */
   public static Coordinate inCentre(Coordinate a, Coordinate b, Coordinate c)
   {
-    // the lengths of the sides, labelled by their opposite vertex
-    double len0 = b.distance(c);
-    double len1 = a.distance(c);
-    double len2 = a.distance(b);
-    double circum = len0 + len1 + len2;
-
-    double inCentreX = (len0 * a.x + len1 * b.x + len2 * c.x) / circum;
-    double inCentreY = (len0 * a.y + len1 * b.y + len2 * c.y) / circum;
+    double lenAB = a.distance(b);
+    double lenBC = b.distance(c);
+    double lenCA = c.distance(a);
+    double circum = lenBC + lenCA + lenAB;
+
+    double inCentreX = (lenBC * a.x + lenCA * b.x + lenAB * c.x) / circum;
+    double inCentreY = (lenBC * a.y + lenCA * b.y + lenAB * c.y) / circum;
     return new Coordinate(inCentreX, inCentreY);
   }
 
@@ -368,9 +367,9 @@ public static Coordinate angleBisector(Coordinate a, Coordinate b,
      * Uses the fact that the lengths of the parts of the split segment are
      * proportional to the lengths of the adjacent triangle sides
      */
-    double len0 = b.distance(a);
-    double len2 = b.distance(c);
-    double frac = len0 / (len0 + len2);
+    double lenBA = b.distance(a);
+    double lenBC = b.distance(c);
+    double frac = lenBA / (lenBA + lenBC);
     double dx = c.x - a.x;
     double dy = c.y - a.y;
 
@@ -393,8 +392,7 @@ public static Coordinate angleBisector(Coordinate a, Coordinate b,
    */
   public static double area(Coordinate a, Coordinate b, Coordinate c)
   {
-    return Math
-        .abs(((c.x - a.x) * (b.y - a.y) - (b.x - a.x) * (c.y - a.y)) / 2);
+    return Math.abs(((c.x - a.x) * (b.y - a.y) - (b.x - a.x) * (c.y - a.y)) / 2);
   }
 
   /**

modules/core/src/test/java/org/locationtech/jts/geom/TriangleTest.java

@@ -11,6 +11,7 @@
  */
 package org.locationtech.jts.geom;
 
+import org.locationtech.jts.algorithm.Distance;
 import org.locationtech.jts.io.WKTReader;
 
 import junit.framework.TestCase;
@@ -167,6 +168,24 @@ public void testCentroid() throws Exception
         (10.0 + 20.0 + 15.0) / 3.0, (10.0 + 10.0 + 20.0) / 3.0));
   }
 
+  public void testInCentre() throws Exception
+  {
+    // right triangle
+    checkInCentre("POLYGON((10 10, 20 20, 20 10, 10 10))", 
+        new Coordinate(17.071067811865476, 12.928932188134524) );
+    // CCW right tri
+    checkInCentre("POLYGON((10 10, 20 10, 20 20, 10 10))", 
+        new Coordinate(17.071067811865476, 12.928932188134524) );
+    // acute
+    checkInCentre("POLYGON((10 10, 20 10, 15 20, 10 10))", 
+        new Coordinate(14.999999999999998, 13.090169943749475));
+    // obtuse
+    checkInCentre("POLYGON ((10 10, 20 10, 40 20, 10 10))", 
+        new Coordinate(19.63104841334295, 11.56290400148567));
+  }
+  
+  //==========================================================
+  
   public void checkCentroid(String wkt, Coordinate expectedValue)
       throws Exception
   {
@@ -185,6 +204,35 @@ public void checkCentroid(String wkt, Coordinate expectedValue)
     assertEquals(expectedValue.toString(), centroid.toString());
   }
 
+  public void checkInCentre(String wkt, Coordinate expectedValue)
+      throws Exception
+  {
+    double tolerance = 0.00001;
+    
+    Geometry g = reader.read(wkt);
+    Coordinate[] pt = g.getCoordinates();
+
+    Coordinate centre = Triangle.inCentre(pt[0], pt[1], pt[2]);
+    //System.out.println("(Static) centroid = " + centroid);
+    checkEqualXY(expectedValue, centre, tolerance);
+    checkEquidistantToEdges(centre, pt, tolerance);
+    
+    // Test Instance version
+    //
+    Triangle t = new Triangle(pt[0], pt[1], pt[2]);
+    Coordinate centreTri = t.inCentre();
+    checkEqualXY(expectedValue, centreTri, tolerance);
+  }
+
+  private void checkEquidistantToEdges(Coordinate centre, Coordinate[] pt, double tolerance) {
+    //-- inCenter must be equidistant from edges
+    double radius0 = Distance.pointToLinePerpendicular(centre, pt[0], pt[1]);
+    double radius1 = Distance.pointToLinePerpendicular(centre, pt[1], pt[2]);
+    double radius2 = Distance.pointToLinePerpendicular(centre, pt[2], pt[3]);
+    assertEquals(radius0, radius1, tolerance);
+    assertEquals(radius0, radius2, tolerance);
+  }
+  
   public void checkCircumCentre(String wkt, Coordinate expectedValue)
       throws Exception
   {