LUCENE-8550: Fix filtering of coplanar points when creating linked list on polygon tesselator

lucene/CHANGES.txt

@@ -238,6 +238,9 @@ Improvements:
 
 Bug Fixes:
 
+* LUCENE-8550: Fix filtering of coplanar points when creating linked list on
+  polygon tesselator. (Ignacio Vera)
+
 * LUCENE-8549: Polygon tessellator throws an error if some parts of the shape
    could not be processed. (Ignacio Vera)
 

lucene/sandbox/src/java/org/apache/lucene/geo/Tessellator.java

@@ -124,15 +124,11 @@ final public class Tessellator {
     // Link points into the circular doubly-linked list in the specified winding order
     if (windingOrder == polygon.getWindingOrder()) {
       for (int i = 0; i < polygon.numPoints(); ++i) {
-        if (lastNode == null || filter(polygon, i, lastNode) == false) {
+        lastNode = insertNode(polygon, startIndex++, i, lastNode);
-          lastNode = insertNode(polygon, startIndex++, i, lastNode);
-        }
       }
     } else {
       for (int i = polygon.numPoints() - 1; i >= 0; --i) {
-        if (lastNode == null || filter(polygon, i, lastNode) == false) {
+        lastNode = insertNode(polygon, startIndex++, i, lastNode);
-          lastNode = insertNode(polygon, startIndex++, i, lastNode);
-        }
       }
     }
     // if first and last node are the same then remove the end node and set lastNode to the start
@@ -142,7 +138,7 @@ final public class Tessellator {
     }
 
     // Return the last node in the Doubly-Linked List
-    return lastNode;
+    return filterPoints(lastNode, null);
   }
 
   /** Links every hole into the outer loop, producing a single-ring polygon without holes. **/
@@ -641,19 +637,6 @@ final public class Tessellator {
     } while (numMerges > 1);
   }
 
-  /** utility method to filter a single duplicate or colinear triangle */
-  private static boolean filter(final Polygon polygon, final int i, final Node node) {
-    final double x = polygon.getPolyLon(i);
-    final double y = polygon.getPolyLat(i);
-    final boolean equal = (x == node.getX() && y == node.getY());
-    if (equal == true) {
-      return true;
-    } else if (node.previous == node || node.previous.previous == node) {
-      return false;
-    }
-    return area(node.previous.previous.getX(), node.previous.previous.getY(), node.previous.getX(), node.previous.getY(), x, y) == 0d;
-  }
-
   /** Eliminate colinear/duplicate points from the doubly linked list */
   private static final Node filterPoints(final Node start, Node end) {
     if (start == null) {

lucene/sandbox/src/test/org/apache/lucene/geo/TestTessellator.java

@@ -90,4 +90,10 @@ public class TestTessellator extends LuceneTestCase {
     Polygon polygon = (Polygon)SimpleWKTShapeParser.parse(wkt);
     expectThrows( IllegalArgumentException.class, () -> {Tessellator.tessellate(polygon); });
   }
+
+  public void testLUCENE8550()  throws Exception {
+    String wkt = "POLYGON((24.04725 59.942,24.04825 59.94125,24.04875 59.94125,24.04875 59.94175,24.048 59.9425,24.0475 59.94275,24.0465 59.94225,24.046 59.94225,24.04575 59.9425,24.04525 59.94225,24.04725 59.942))";
+    Polygon polygon = (Polygon)SimpleWKTShapeParser.parse(wkt);
+    assertTrue(Tessellator.tessellate(polygon).size() == 8);
+  }
 }