Class KdTree
- java.lang.Object
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- org.locationtech.jts.index.kdtree.KdTree
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public class KdTree extends java.lang.Object
An implementation of a KD-Tree over two dimensions (X and Y). KD-trees provide fast range searching and fast lookup for point data. The tree is built dynamically by inserting points. The tree supports queries by range and for point equality. For querying an internal stack is used instead of recursion to avoid overflow.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 an inserted 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.
The structure of a KD-Tree depends on the order of insertion of the points. A tree may become unbalanced if the inserted points are coherent (e.g. monotonic in one or both dimensions). A perfectly balanced tree has depth of only log2(N), but an unbalanced tree may be much deeper. This has a serious impact on query efficiency. One solution to this is to randomize the order of points before insertion (e.g. by using Fisher-Yates shuffling).
- Author:
- David Skea, Martin Davis
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description int
depth()
Computes the depth of the tree.KdNode
getRoot()
Gets the root node of this tree.KdNode
insert(Coordinate p)
Inserts a new point in the kd-tree, with no data.KdNode
insert(Coordinate p, java.lang.Object data)
Inserts a new point into the kd-tree.boolean
isEmpty()
Tests whether the index contains any items.KdNode
query(Coordinate queryPt)
Searches for a given point in the index and returns its node if found.java.util.List
query(Envelope queryEnv)
Performs a range search of the points in the index.void
query(Envelope queryEnv, java.util.List result)
Performs a range search of the points in the index.void
query(Envelope queryEnv, KdNodeVisitor visitor)
Performs a range search of the points in the index and visits all nodes found.int
size()
Computes the size (number of items) in the tree.static Coordinate[]
toCoordinates(java.util.Collection kdnodes)
Converts a collection ofKdNode
s to an array ofCoordinate
s.static Coordinate[]
toCoordinates(java.util.Collection kdnodes, boolean includeRepeated)
Converts a collection ofKdNode
s to an array ofCoordinate
s, specifying whether repeated nodes should be represented by multiple coordinates.
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Constructor Detail
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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)
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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
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Method Detail
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toCoordinates
public static Coordinate[] toCoordinates(java.util.Collection kdnodes)
Converts a collection ofKdNode
s to an array ofCoordinate
s.- Parameters:
kdnodes
- a collection of nodes- Returns:
- an array of the coordinates represented by the nodes
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toCoordinates
public static Coordinate[] toCoordinates(java.util.Collection kdnodes, boolean includeRepeated)
Converts a collection ofKdNode
s to an array ofCoordinate
s, specifying whether repeated nodes should be represented by multiple coordinates.- Parameters:
kdnodes
- a collection of nodesincludeRepeated
- true if repeated nodes should be included multiple times- Returns:
- an array of the coordinates represented by the nodes
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getRoot
public KdNode getRoot()
Gets the root node of this tree.- Returns:
- the root node of the tree
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isEmpty
public boolean isEmpty()
Tests whether the index contains any items.- Returns:
- true if the index does not contain any items
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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
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insert
public KdNode insert(Coordinate p, java.lang.Object data)
Inserts a new point into the kd-tree.- Parameters:
p
- the point to insertdata
- 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.
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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 queryvisitor
- a visitor to visit all nodes found by the search
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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
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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 queryresult
- a list to accumulate the result nodes into
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query
public KdNode query(Coordinate queryPt)
Searches for a given point in the index and returns its node if found.- Parameters:
queryPt
- the point to query- Returns:
- the point node, if it is found in the index, or null if not
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depth
public int depth()
Computes the depth of the tree.- Returns:
- the depth of the tree
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size
public int size()
Computes the size (number of items) in the tree.- Returns:
- the size of the tree
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