From a3d190e4a1492d127addf42dea914e858f9d8c59 Mon Sep 17 00:00:00 2001
From: Martin Davis <mtnclimb@gmail.com>
Date: Fri, 3 Jan 2025 16:45:17 -0800
Subject: [PATCH] Fix VWSimplifier coordinate aliasing

---
 .../jts/simplify/VWLineSimplifier.java          |  5 +++--
 .../jts/simplify/VWSimplifierTest.java          | 11 +++++++++--
 .../test/java/test/jts/GeometryTestCase.java    | 17 +++++++++++++++++
 3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/modules/core/src/main/java/org/locationtech/jts/simplify/VWLineSimplifier.java b/modules/core/src/main/java/org/locationtech/jts/simplify/VWLineSimplifier.java
index c5f974b8c8..2126e17e4f 100644
--- a/modules/core/src/main/java/org/locationtech/jts/simplify/VWLineSimplifier.java
+++ b/modules/core/src/main/java/org/locationtech/jts/simplify/VWLineSimplifier.java
@@ -13,6 +13,7 @@
 package org.locationtech.jts.simplify;
 
 import org.locationtech.jts.geom.Coordinate;
+import org.locationtech.jts.geom.CoordinateArrays;
 import org.locationtech.jts.geom.CoordinateList;
 import org.locationtech.jts.geom.Triangle;
 
@@ -51,9 +52,9 @@ public Coordinate[] simplify()
     Coordinate[] simp = vwLine.getCoordinates();
     // ensure computed value is a valid line
     if (simp.length < 2) {
-      return new Coordinate[] { simp[0], new Coordinate(simp[0]) };
+      return new Coordinate[] { simp[0].copy(), simp[0].copy() };
     }
-    return simp;
+    return CoordinateArrays.copyDeep(simp);
   }
 
   private double simplifyVertex(VWLineSimplifier.VWVertex vwLine)
diff --git a/modules/core/src/test/java/org/locationtech/jts/simplify/VWSimplifierTest.java b/modules/core/src/test/java/org/locationtech/jts/simplify/VWSimplifierTest.java
index 28e3a427dc..32b2c0079e 100644
--- a/modules/core/src/test/java/org/locationtech/jts/simplify/VWSimplifierTest.java
+++ b/modules/core/src/test/java/org/locationtech/jts/simplify/VWSimplifierTest.java
@@ -12,18 +12,20 @@
 
 package org.locationtech.jts.simplify;
 
+import org.locationtech.jts.geom.Coordinate;
+import org.locationtech.jts.geom.CoordinateFilter;
 import org.locationtech.jts.geom.Geometry;
 import org.locationtech.jts.io.ParseException;
 import org.locationtech.jts.io.WKTReader;
 
-import junit.framework.TestCase;
+import test.jts.GeometryTestCase;
 
 
 /**
  * @version 1.7
  */
 public class VWSimplifierTest
-    extends TestCase
+    extends GeometryTestCase
 {
   public VWSimplifierTest(String name) {
     super(name);
@@ -67,6 +69,11 @@ public void testPolygonSpikeInHole() throws Exception {
         .test();
   }
 
+  public void testNoAlias() {
+    Geometry geom = read("LINESTRING (1 1, 3 6, 6 5, 8 6, 9 1)");
+    Geometry result = VWSimplifier.simplify(geom, 2);
+    checkNoAlias(geom, result);
+  }
  
 }
 
diff --git a/modules/core/src/test/java/test/jts/GeometryTestCase.java b/modules/core/src/test/java/test/jts/GeometryTestCase.java
index 8b308719a5..8b51fd91f9 100644
--- a/modules/core/src/test/java/test/jts/GeometryTestCase.java
+++ b/modules/core/src/test/java/test/jts/GeometryTestCase.java
@@ -38,6 +38,7 @@ public abstract class GeometryTestCase extends TestCase{
 
   private static final String CHECK_EQUAL_FAIL = "FAIL - Expected = %s -- Actual = %s\n";
   private static final String CHECK_EQUAL_FAIL_MSG = "FAIL - %s: Expected = %s -- Actual = %s\n";
+  private static final String CHECK_NO_AlIAS_FAIL = "FAIL - geometries have aliased coordinates\n";
 
   final GeometryFactory geomFactory;
   
@@ -225,6 +226,22 @@ protected void checkEqualXY(String message, Coordinate expected, Coordinate actu
     assertEquals(message + " Y", expected.getY(), actual.getY(), tolerance);
   }
  
+  protected void checkNoAlias(Geometry geom, Geometry geom2) {
+    Geometry geom2Copy = geom2.copy();
+    geom.apply(new CoordinateFilter() {
+
+      @Override
+      public void filter(Coordinate coord) {
+        coord.x = coord.x + 1;
+      }
+      
+    });
+    boolean equal = geom2.equalsExact(geom2Copy);
+    if (! equal) {
+      System.out.println(CHECK_NO_AlIAS_FAIL);
+      fail();
+    }
+  }
   
   /**
    * Reads a {@link Geometry} from a WKT string using a custom {@link GeometryFactory}.