Fix vertex-vertex intersection in OverlayArea

modules/lab/src/main/java/org/locationtech/jts/operation/overlayarea/OverlayArea.java

@@ -268,17 +268,27 @@ private static double areaForIntersection(Coordinate a0, Coordinate a1, Coordina
      * For accuracy the full edge is used to provide the direction vector.
      */
     Coordinate intPt = li.getIntersection(0);
-
-    boolean isAenteringB = Orientation.COUNTERCLOCKWISE == Orientation.index(a0, a1, b1);
-
-    if ( isAenteringB ) {
+
+    if ( Orientation.CLOCKWISE == Orientation.index(a0, a1, b0) ) {
+      if (intPt.equals2D(a1)) {
+        // Intersection at vertex and A0 -> A1 is outside of the intersection area
+        // Area will be computed by the segment A1 -> A2
+        return 0.0;
+      }
       return EdgeVector.area2Term(intPt, a0, a1, true)
         + EdgeVector.area2Term(intPt, b1, b0, false);
     }
-    else {
+    else if ( Orientation.CLOCKWISE == Orientation.index(a0, a1, b1) ) {
+      if (intPt.equals2D(a0)) {
+        // Intersection at vertex and A0 -> A1 is outside of the intersection area
+        // Area will be computed by the segment A(-1) -> A0
+        return 0.0;
+      }
       return EdgeVector.area2Term(intPt, a1, a0, false)
        + EdgeVector.area2Term(intPt, b0, b1, true);
     }
+
+    return 0.0;
   }
 
   private double areaForInteriorVertices(LinearRing ring) {

modules/lab/src/main/java/org/locationtech/jts/operation/overlayarea/SimpleOverlayArea.java

@@ -116,14 +116,22 @@ private double areaForIntersections(CoordinateSequence ringA, boolean isCCWA, Co
            * Use full edge to compute direction, for accuracy.
            */
           Coordinate intPt = li.getIntersection(0);
-
-          boolean isAenteringB = Orientation.COUNTERCLOCKWISE == Orientation.index(a0, a1, b1);
-
-          if ( isAenteringB ) {
+
+          if ( Orientation.CLOCKWISE == Orientation.index(a0, a1, b0) ) {
+            if (intPt.equals2D(a1)) {
+              // Intersection at vertex and A0 -> A1 is outside of the intersection area
+              // Area will be computed by the segment A1 -> A2
+              continue;
+            }
             area += EdgeVector.area2Term(intPt, a0, a1, true);
             area += EdgeVector.area2Term(intPt, b1, b0, false);
           }
-          else {
+          else if ( Orientation.CLOCKWISE == Orientation.index(a0, a1, b1) ) {
+            if (intPt.equals2D(a0)) {
+              // Intersection at vertex and A0 -> A1 is outside of the intersection area
+              // Area will be computed by the segment A(-1) -> A0
+              continue;
+            }
             area += EdgeVector.area2Term(intPt, a1, a0, false);
             area += EdgeVector.area2Term(intPt, b0, b1, true);
           }

modules/lab/src/test/java/org/locationtech/jts/operation/overlayarea/OverlayAreaTest.java

@@ -31,13 +31,24 @@ public void testDisjoint() {
         "POLYGON ((10 90, 40 90, 40 60, 10 60, 10 90))",
         "POLYGON ((90 10, 50 10, 50 50, 90 50, 90 10))");
   }
-
-  //TODO: fix this bug
-  public void xtestTouching() {
+
+  public void testTouchingTwoCollinear() {
     checkIntersectionArea(
         "POLYGON ((10 90, 50 90, 50 50, 10 50, 10 90))",
         "POLYGON ((90 10, 50 10, 50 50, 90 50, 90 10))");
   }
+
+  public void testTouchingOneCollinear() {
+    checkIntersectionArea(
+        "POLYGON ((10 90, 50 90, 50 50, 10 50, 10 90))",
+        "POLYGON ((90 10, 49 10, 50 50, 90 50, 90 10))");
+  }
+
+  public void testTouchingNoneCollinear() {
+    checkIntersectionArea(
+        "POLYGON ((10 90, 50 90, 50 50, 10 52, 10 90))",
+        "POLYGON ((90 10, 49 10, 50 50, 90 50, 90 10))");
+  }
 
   public void testRectangleAContainsB() {
     checkIntersectionArea(

modules/lab/src/test/java/org/locationtech/jts/operation/overlayarea/SimpleOverlayAreaTest.java

@@ -32,13 +32,24 @@ public void testDisjoint() {
         "POLYGON ((90 10, 50 10, 50 50, 90 50, 90 10))");
   }
 
-  //TODO: fix this bug
-  public void xtestTouching() {
+  public void testTouchingTwoCollinear() {
     checkIntersectionArea(
         "POLYGON ((10 90, 50 90, 50 50, 10 50, 10 90))",
         "POLYGON ((90 10, 50 10, 50 50, 90 50, 90 10))");
   }
 
+  public void testTouchingOneCollinear() {
+    checkIntersectionArea(
+        "POLYGON ((10 90, 50 90, 50 50, 10 50, 10 90))",
+        "POLYGON ((90 10, 49 10, 50 50, 90 50, 90 10))");
+  }
+
+  public void testTouchingNoneCollinear() {
+    checkIntersectionArea(
+        "POLYGON ((10 90, 50 90, 50 50, 10 52, 10 90))",
+        "POLYGON ((90 10, 49 10, 50 50, 90 50, 90 10))");
+  }
+
   public void testRectangleAContainsB() {
     checkIntersectionArea(
         "POLYGON ((100 300, 300 300, 300 100, 100 100, 100 300))",