making NearestNeighbor for kd tree search properly.

It was just checking to see if the left or right tree had a better score than current but the algorithm should check to see if the planes cross our best score for the coordinate we are looking for, not if the nodes score is better or not.

Author: lloydstockman

NetTopologySuite.Tests.NUnit/Index/KdTree/KdTreeTest.cs

@@ -68,7 +68,6 @@ public void TestNearestNeighbor()
             kd.Insert(new Coordinate(19, 12), "J");
             kd.Insert(new Coordinate(10, 2), "K");
 
-
             var res = kd.NearestNeighbor(new Coordinate(13, 2));
 
             Assert.AreEqual("K", res.Data);

NetTopologySuite/Index/KdTree/KdTree.cs

@@ -337,12 +337,10 @@ private static void NearestNeighbor(KdNode<T> currentNode,
                 var searchLeft = false;
                 var searchRight = false;
                 if (currentNode.Left != null)
-                    searchLeft = (Math.Pow(currentNode.Left.X - queryCoordinate.X, 2) +
-                                  Math.Pow(currentNode.Left.Y - queryCoordinate.Y, 2)) < closestDistanceSq;
+                    searchLeft = NeedsToBeSearched(queryCoordinate, currentNode.Left, closestDistanceSq);
 
                 if (currentNode.Right != null)
-                    searchRight = (Math.Pow(currentNode.Right.X - queryCoordinate.X, 2) +
-                                   Math.Pow(currentNode.Right.Y - queryCoordinate.Y, 2)) < closestDistanceSq;
+                    searchRight = NeedsToBeSearched(queryCoordinate, currentNode.Right, closestDistanceSq);
 
                 if (searchLeft)
                 {
@@ -359,6 +357,12 @@ private static void NearestNeighbor(KdNode<T> currentNode,
             }
         }
 
+        private static bool NeedsToBeSearched(Coordinate target, KdNode<T> node, double closestDistSq)
+        {
+            return node.X >= target.X - closestDistSq && node.X <= target.X + closestDistSq
+                || node.Y >= target.Y - closestDistSq && node.Y <= target.Y + closestDistSq;
+        }
+
         /// <summary>
         /// Performs a nearest neighbor search of the points in the index.
         /// </summary>