Fix OverlayNG strict mode Union bug

Signed-off-by: Martin Davis <mtnclimb@gmail.com>
dr-jts · Sep 16, 2020 · b0d6f03 · b0d6f03
1 parent dabe23c
commit b0d6f03
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Showing 2 changed files with 37 additions and 19 deletions.
diff --git a/modules/core/src/main/java/org/locationtech/jts/operation/overlayng/OverlayNG.java b/modules/core/src/main/java/org/locationtech/jts/operation/overlayng/OverlayNG.java
@@ -70,17 +70,20 @@
  * since the intersection clipping optimization can 
  * interact with the snapping to alter the result.
  * <p>
- * There is an option to set the overlay computation to work in strict mode.
- * In strict mode results have the following semantics:
+ * Optionally the overlay computation can process using strict mode
+ * (via {@link #setStrictMode(boolean)}.
+ * In strict mode result semantics are:
  * <ul>
- * <li>Result geometries are homogeneous (all components are of same dimension)
- * <li>Lines resulting from topology collapses are not included in the result
+ * <li>Result geometries are homogeneous (all components are of same dimension),
+ *     except for some cases of symmetricDifference.
+ * <li>Lines and Points resulting from topology collapses are not included in the result
  * </ul>
  * Strict mode has the following benefits:
  * <ul>
+ * <li>Results are simpler
  * <li>Overlay operations are easily chainable
  * </ul>
- * The original JTS overlay semantics correspons to non-strict mode.
+ * The original JTS overlay semantics corresponds to non-strict mode.
  * 
  * @author mdavis
  * 
@@ -557,7 +560,8 @@ private Geometry extractResult(int opCode, OverlayGraph graph) {
       //--- Build lines
       boolean allowResultLines = ! hasResultAreaComponents 
           || isAllowMixedIntResult
-          || opCode == SYMDIFFERENCE;
+          || opCode == SYMDIFFERENCE
+          || opCode == UNION;
       if ( allowResultLines ) {
         LineBuilder lineBuilder = new LineBuilder(inputGeom, graph, hasResultAreaComponents, opCode, geomFact);
         lineBuilder.setStrictMode(isStrictMode);

diff --git a/.../core/src/test/java/org/locationtech/jts/operation/overlayng/OverlayNGStrictModeTest.java b/.../core/src/test/java/org/locationtech/jts/operation/overlayng/OverlayNGStrictModeTest.java
@@ -78,6 +78,14 @@ public void testPolygonLineSymDifference() {
     checkEqual(expected, actual);
   }
 
+  public void testPolygonLineUnion() {
+    Geometry a = read("POLYGON ((10 20, 20 20, 20 10, 10 10, 10 20))");
+    Geometry b = read("LINESTRING (15 15, 25 15)");
+    Geometry expected = read("GEOMETRYCOLLECTION (POLYGON ((20 20, 20 15, 20 10, 10 10, 10 20, 20 20)), LINESTRING (20 15, 25 15))");
+    Geometry actual = union(a, b);
+    checkEqual(expected, actual);
+  }
+
   /**
    * Check that result does not include collapsed line intersection
    */
@@ -97,27 +105,33 @@ public void testPolygonUnionCollapse() {
     checkEqual(expected, actual);
   }
 
-  public static Geometry intersection(Geometry a, Geometry b) {
-    OverlayNG ov = new OverlayNG(a, b, INTERSECTION);
-    ov.setStrictMode(true);
-    return ov.getResult();
+  static Geometry intersection(Geometry a, Geometry b) {
+    return overlay(a, b, INTERSECTION);
   }
 
-  public static Geometry symDifference(Geometry a, Geometry b) {
-    OverlayNG ov = new OverlayNG(a, b, SYMDIFFERENCE);
-    ov.setStrictMode(true);
-    return ov.getResult();
+  static Geometry symDifference(Geometry a, Geometry b) {
+    return overlay(a, b, SYMDIFFERENCE);
   }
 
-  public static Geometry intersection(Geometry a, Geometry b, double scaleFactor) {
-    PrecisionModel pm = new PrecisionModel(scaleFactor);
-    OverlayNG ov = new OverlayNG(a, b, pm, INTERSECTION);
+  static Geometry union(Geometry a, Geometry b) {
+    return overlay(a, b, UNION);
+  }
+
+  static Geometry overlay(Geometry a, Geometry b, int opCode) {
+    OverlayNG ov = new OverlayNG(a, b, opCode);
     ov.setStrictMode(true);
     return ov.getResult();
   }
-  public static Geometry union(Geometry a, Geometry b, double scaleFactor) {
+
+  static Geometry intersection(Geometry a, Geometry b, double scaleFactor) {
+    return overlay(a, b, scaleFactor, INTERSECTION);
+  }
+  static Geometry union(Geometry a, Geometry b, double scaleFactor) {
+    return overlay(a, b, scaleFactor, UNION);
+  }
+  static Geometry overlay(Geometry a, Geometry b, double scaleFactor, int opCode) {
     PrecisionModel pm = new PrecisionModel(scaleFactor);
-    OverlayNG ov = new OverlayNG(a, b, pm, UNION);
+    OverlayNG ov = new OverlayNG(a, b, pm, opCode);
     ov.setStrictMode(true);
     return ov.getResult();
   }