Class KdTree


  • public class KdTree
    extends java.lang.Object
    An implementation of a 2-D KD-Tree. KD-trees provide fast range searching on point data.

    This implementation supports detecting and snapping points which are closer than a given distance tolerance. If the same point (up to tolerance) is inserted more than once, it is snapped to the existing node. In other words, if a point is inserted which lies within the tolerance of a node already in the index, it is snapped to that node. When a point is snapped to a node then a new node is not created but the count of the existing node is incremented. If more than one node in the tree is within tolerance of an inserted point, the closest and then lowest node is snapped to.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private static class  KdTree.BestMatchVisitor  
    • Constructor Summary

      Constructors 
      Constructor Description
      KdTree()
      Creates a new instance of a KdTree with a snapping tolerance of 0.0.
      KdTree​(double tolerance)
      Creates a new instance of a KdTree, specifying a snapping distance tolerance.
    • Field Detail

      • numberOfNodes

        private long numberOfNodes
      • tolerance

        private double tolerance
    • Constructor Detail

      • KdTree

        public KdTree()
        Creates a new instance of a KdTree with a snapping tolerance of 0.0. (I.e. distinct points will not be snapped)
      • KdTree

        public KdTree​(double tolerance)
        Creates a new instance of a KdTree, specifying a snapping distance tolerance. Points which lie closer than the tolerance to a point already in the tree will be treated as identical to the existing point.
        Parameters:
        tolerance - the tolerance distance for considering two points equal
    • Method Detail

      • toCoordinates

        public static Coordinate[] toCoordinates​(java.util.Collection kdnodes)
        Converts a collection of KdNodes to an array of Coordinates.
        Parameters:
        kdnodes - a collection of nodes
        Returns:
        an array of the coordinates represented by the nodes
      • toCoordinates

        public static Coordinate[] toCoordinates​(java.util.Collection kdnodes,
                                                 boolean includeRepeated)
        Converts a collection of KdNodes to an array of Coordinates, specifying whether repeated nodes should be represented by multiple coordinates.
        Parameters:
        kdnodes - a collection of nodes
        includeRepeated - true if repeated nodes should be included multiple times
        Returns:
        an array of the coordinates represented by the nodes
      • isEmpty

        public boolean isEmpty()
        Tests whether the index contains any items.
        Returns:
        true if the index does not contain any items
      • insert

        public KdNode insert​(Coordinate p)
        Inserts a new point in the kd-tree, with no data.
        Parameters:
        p - the point to insert
        Returns:
        the kdnode containing the point
      • insert

        public KdNode insert​(Coordinate p,
                             java.lang.Object data)
        Inserts a new point into the kd-tree.
        Parameters:
        p - the point to insert
        data - a data item for the point
        Returns:
        returns a new KdNode if a new point is inserted, else an existing node is returned with its counter incremented. This can be checked by testing returnedNode.getCount() > 1.
      • findBestMatchNode

        private KdNode findBestMatchNode​(Coordinate p)
        Finds the node in the tree which is the best match for a point being inserted. The match is made deterministic by returning the lowest of any nodes which lie the same distance from the point. There may be no match if the point is not within the distance tolerance of any existing node.
        Parameters:
        p - the point being inserted
        Returns:
        the best matching node
      • insertExact

        private KdNode insertExact​(Coordinate p,
                                   java.lang.Object data)
        Inserts a point known to be beyond the distance tolerance of any existing node. The point is inserted at the bottom of the exact splitting path, so that tree shape is deterministic.
        Parameters:
        p - the point to insert
        data - the data for the point
        Returns:
        the created node
      • query

        public void query​(Envelope queryEnv,
                          KdNodeVisitor visitor)
        Performs a range search of the points in the index and visits all nodes found.
        Parameters:
        queryEnv - the range rectangle to query
        visitor - a visitor to visit all nodes found by the search
      • query

        public java.util.List query​(Envelope queryEnv)
        Performs a range search of the points in the index.
        Parameters:
        queryEnv - the range rectangle to query
        Returns:
        a list of the KdNodes found
      • query

        public void query​(Envelope queryEnv,
                          java.util.List result)
        Performs a range search of the points in the index.
        Parameters:
        queryEnv - the range rectangle to query
        result - a list to accumulate the result nodes into