Class Quadtree

Hierarchy: Object , Quadtree

All Implemented Interfaces: SpatialIndex, Serializable

public class Quadtree
implements Serializable , SpatialIndex

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 accommodate any extent of dataset.

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

Other

version: 1.7

public Quadtree()

Constructs a Quadtree with zero items.

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

public int depth()

Returns the number of levels in the tree.

public boolean isEmpty()

Tests whether the index contains any items.

Returns:: true if the index does not contain any items

public int size()

Returns the number of items in the tree.

Returns:: the number of items in the tree

public void insert(Envelope itemEnv, Object item)

public boolean remove(Envelope itemEnv, Object item)

Removes a single item from the tree.

Parameters:: itemEnv - itemEnv the Envelope of the item to be removed; item - item the item to remove

Returns:: true if the item was found (and thus removed)

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.

Parameters:: searchEnv - searchEnv the envelope of the desired query area.

Returns:: a List of items which may intersect the search envelope

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.

Parameters:: searchEnv - searchEnv the envelope of the desired query area.; visitor - visitor a visitor object which is passed the visited items

public List queryAll()

Return a list of all items in the Quadtree