com.vividsolutions.jts.index.quadtree

Class Quadtree

java.lang.Object

com.vividsolutions.jts.index.quadtree.Quadtree

All Implemented Interfaces:

SpatialIndex, Serializable

public class Quadtree
extends Object
implements SpatialIndex, Serializable

A Quadtree is a spatial index structure for efficient range querying of items bounded by 2D rectangles. Geometrys can be indexed by using their Envelopes. Any type of Object can also be indexed as long as it has an extent that can be represented by an Envelope.

This Quadtree index provides a primary filter for range rectangle queries. The various query methods return a list of all items which may intersect the query rectangle. Note that it may thus return items which do not in fact intersect the query rectangle. A secondary filter is required to test for actual intersection between the query rectangle and the envelope of each candidate item. The secondary filter may be performed explicitly, or it may be provided implicitly by subsequent operations executed on the items (for instance, if the index query is followed by computing a spatial predicate between the query geometry and tree items, the envelope intersection check is performed automatically.

This implementation does not require specifying the extent of the inserted items beforehand. It will automatically expand to accomodate any extent of dataset.

This data structure is also known as an MX-CIF quadtree following the terminology of Samet and others.

Version:

1.7

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Quadtree() Constructs a Quadtree with zero items.

Method Summary

Modifier and Type	Method and Description
int	depth() Returns the number of levels in the tree.
static Envelope	ensureExtent(Envelope itemEnv, double minExtent) Ensure that the envelope for the inserted item has non-zero extents.
void	insert(Envelope itemEnv, Object item) Adds a spatial item with an extent specified by the given Envelope to the index
boolean	isEmpty() Tests whether the index contains any items.
List	query(Envelope searchEnv) Queries the tree and returns items which may lie in the given search envelope.
void	query(Envelope searchEnv, ItemVisitor visitor) Queries the tree and visits items which may lie in the given search envelope.
List	queryAll() Return a list of all items in the Quadtree
boolean	remove(Envelope itemEnv, Object item) Removes a single item from the tree.
int	size() Returns the number of items in the tree.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Quadtree

public Quadtree()

Constructs a Quadtree with zero items.

Method Detail

ensureExtent

public static Envelope ensureExtent(Envelope itemEnv,
                                    double minExtent)

Ensure that the envelope for the inserted item has non-zero extents. Use the current minExtent to pad the envelope, if necessary

depth

public int depth()

Returns the number of levels in the tree.

isEmpty

public boolean isEmpty()

Tests whether the index contains any items.

Returns:

true if the index does not contain any items

size

public int size()

Returns the number of items in the tree.

Returns:

the number of items in the tree

insert

public void insert(Envelope itemEnv,
                   Object item)

Description copied from interface: SpatialIndex

Adds a spatial item with an extent specified by the given Envelope to the index

Specified by:

insert in interface SpatialIndex

remove

public boolean remove(Envelope itemEnv,
                      Object item)

Removes a single item from the tree.

Specified by:

remove in interface SpatialIndex

Parameters:

itemEnv - the Envelope of the item to be removed

item - the item to remove

Returns:

true if the item was found (and thus removed)

query

public List query(Envelope searchEnv)

Queries the tree and returns items which may lie in the given search envelope. Precisely, the items that are returned are all items in the tree whose envelope may intersect the search Envelope. Note that some items with non-intersecting envelopes may be returned as well; the client is responsible for filtering these out. In most situations there will be many items in the tree which do not intersect the search envelope and which are not returned - thus providing improved performance over a simple linear scan.

Specified by:

query in interface SpatialIndex

Parameters:

searchEnv - the envelope of the desired query area.

Returns:

a List of items which may intersect the search envelope

query

public void query(Envelope searchEnv,
                  ItemVisitor visitor)

Queries the tree and visits items which may lie in the given search envelope. Precisely, the items that are visited are all items in the tree whose envelope may intersect the search Envelope. Note that some items with non-intersecting envelopes may be visited as well; the client is responsible for filtering these out. In most situations there will be many items in the tree which do not intersect the search envelope and which are not visited - thus providing improved performance over a simple linear scan.

Specified by:

query in interface SpatialIndex

Parameters:

searchEnv - the envelope of the desired query area.

visitor - a visitor object which is passed the visited items

queryAll

public List queryAll()

Return a list of all items in the Quadtree