Class QuadTree<T>

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

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 usage of Samet and others.

Inheritance
System.Object
QuadTree<T>
Namespace: Mars.Common.Collections
Assembly: Mars.Common.dll
Syntax
public class QuadTree<T> : object
Type Parameters
Name Description
T

Constructors

QuadTree()

Creates a new empty QuadTree<T>.
Declaration
public QuadTree()

Properties

Count

Returns the number of items in the tree.
Declaration
public int Count { get; }
Property Value
Type Description
System.Int32

Depth

Returns the number of levels in the tree.
Declaration
public int Depth { get; }
Property Value
Type Description
System.Int32

IsEmpty

Tests whether the index contains any items.
Declaration
public bool IsEmpty { get; }
Property Value
Type Description
System.Boolean

Methods

Insert(Envelope, T)

Declaration
public void Insert(Envelope itemEnv, T item)
Parameters
Type Name Description
Envelope itemEnv
T item

Query(Envelope)

Queries the tree and returns items which may lie in the given search envelope.
Declaration
public IList<T> Query(Envelope searchEnv)
Parameters
Type Name Description
Envelope searchEnv The envelope of the desired query area.
Returns
Type Description
IList<T> A List of items which may intersect the search envelope
Remarks
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.

Query(Envelope, Action<T>)

Queries the tree and visits items which may lie in the given search envelope.
Declaration
public void Query(Envelope searchEnv, Action<T> visitor)
Parameters
Type Name Description
Envelope searchEnv The envelope of the desired query area.
Action<T> visitor A visitor object which is passed the visited items
Remarks
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.

QueryAll()

Return a list of all items in the QuadTree<T>.
Declaration
public IList<T> QueryAll()
Returns
Type Description
IList<T>

Remove(Envelope, T)

Removes a single item from the tree.
Declaration
public bool Remove(Envelope itemEnv, T item)
Parameters
Type Name Description
Envelope itemEnv The Envelope of the item to be removed.
T item The item to remove.
Returns
Type Description
System.Boolean true if the item was found (and thus removed).