Class STRtree<TItem>

A query-only R-tree created using the Sort-Tile-Recursive (STR) algorithm. For two-dimensional spatial data.

The STR packed R-tree is simple to implement and maximizes space utilization; that is, as many leaves as possible are filled to capacity. Overlap between nodes is far less than in a basic R-tree. However, the index is semi-static; once the tree has been built (which happens automatically upon the first query), items may not be added.
Items may be removed from the tree using Remove(Envelope, TItem).

Described in: P. Rigaux, Michel Scholl and Agnes Voisard. Spatial Databases With Application To GIS. Morgan Kaufmann, San Francisco, 2002.

Note that inserting items into a tree is not thread-safe. Inserting performed on more than one thread must be synchronized externally.

Querying a tree is thread-safe. The building phase is done synchronously, and querying is stateless.
Inheritance
object
AbstractSTRtree<Envelope, TItem>
STRtree<TItem>
Implements
Inherited Members
Namespace: NetTopologySuite.Index.Strtree
Assembly: NetTopologySuite.dll
Syntax
[Serializable]
public class STRtree<TItem> : AbstractSTRtree<Envelope, TItem>, ISpatialIndex<TItem>
Type Parameters
Name Description
TItem

Constructors

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STRtree()

Constructs an STRtree with the default (10) node capacity.

Declaration
public STRtree()
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STRtree(int)

Constructs an STRtree with the given maximum number of child nodes that a node may have.

Declaration
public STRtree(int nodeCapacity)
Parameters
Type Name Description
int nodeCapacity
Remarks

The minimum recommended capacity setting is 4.

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STRtree(int, AbstractNode<Envelope, TItem>)

Constructs an AbstractSTRtree with the specified maximum number of child nodes that a node may have, and the root node

Declaration
public STRtree(int nodeCapacity, AbstractNode<Envelope, TItem> root)
Parameters
Type Name Description
int nodeCapacity

The maximum number of child nodes in a node
AbstractNode<Envelope, TItem> root

The root node that links to all other nodes in the tree
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STRtree(int, IList<IBoundable<Envelope, TItem>>)

Constructs an AbstractSTRtree with the specified maximum number of child nodes that a node may have, and all leaf nodes in the tree

Declaration
public STRtree(int nodeCapacity, IList<IBoundable<Envelope, TItem>> itemBoundables)
Parameters
Type Name Description
int nodeCapacity

The maximum number of child nodes in a node
IList<IBoundable<Envelope, TItem>> itemBoundables

The list of leaf nodes in the tree

Properties

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IntersectsOp

Declaration
protected override AbstractSTRtree<Envelope, TItem>.IIntersectsOp IntersectsOp { get; }
Property Value
Type Description
AbstractSTRtree<Envelope, TItem>.IIntersectsOp
Overrides

Methods

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CreateNode(int)

Declaration
protected override AbstractNode<Envelope, TItem> CreateNode(int level)
Parameters
Type Name Description
int level
Returns
Type Description
AbstractNode<Envelope, TItem>
Overrides
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CreateParentBoundables(IList<IBoundable<Envelope, TItem>>, int)

Creates the parent level for the given child level. First, orders the items by the x-values of the midpoints, and groups them into vertical slices. For each slice, orders the items by the y-values of the midpoints, and group them into runs of size M (the node capacity). For each run, creates a new (parent) node.

Declaration
protected override IList<IBoundable<Envelope, TItem>> CreateParentBoundables(IList<IBoundable<Envelope, TItem>> childBoundables, int newLevel)
Parameters
Type Name Description
IList<IBoundable<Envelope, TItem>> childBoundables
int newLevel
Returns
Type Description
IList<IBoundable<Envelope, TItem>>
Overrides
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CreateParentBoundablesFromVerticalSlice(IList<IBoundable<Envelope, TItem>>, int)

Declaration
protected IList<IBoundable<Envelope, TItem>> CreateParentBoundablesFromVerticalSlice(IList<IBoundable<Envelope, TItem>> childBoundables, int newLevel)
Parameters
Type Name Description
IList<IBoundable<Envelope, TItem>> childBoundables
int newLevel
Returns
Type Description
IList<IBoundable<Envelope, TItem>>
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GetComparer()

Declaration
protected override IComparer<IBoundable<Envelope, TItem>> GetComparer()
Returns
Type Description
IComparer<IBoundable<Envelope, TItem>>
Overrides
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Insert(Envelope, TItem)

Inserts an item having the given bounds into the tree.

Declaration
public void Insert(Envelope itemEnv, TItem item)
Parameters
Type Name Description
Envelope itemEnv
TItem item
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IsWithinDistance(STRtree<TItem>, IItemDistance<Envelope, TItem>, double)

Tests whether some two items from this tree and another tree lie within a given distance. IItemDistance<T, TItem> is used as the distance metric. A Branch-and-Bound tree traversal algorithm is used to provide an efficient search.

Declaration
public bool IsWithinDistance(STRtree<TItem> tree, IItemDistance<Envelope, TItem> itemDist, double maxDistance)
Parameters
Type Name Description
STRtree<TItem> tree

Another tree
IItemDistance<Envelope, TItem> itemDist

A distance metric applicable to the items in the trees
double maxDistance

The distance limit for the search
Returns
Type Description
bool

true if there are items within the distance
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NearestNeighbour(Envelope, TItem, IItemDistance<Envelope, TItem>)

Finds the item in this tree which is nearest to the given item, using IItemDistance<T, TItem> as the distance metric. A Branch-and-Bound tree traversal algorithm is used to provide an efficient search.

The query item does not have to be contained in the tree, but it does have to be compatible with the itemDist distance metric.
Declaration
public TItem NearestNeighbour(Envelope env, TItem item, IItemDistance<Envelope, TItem> itemDist)
Parameters
Type Name Description
Envelope env

The envelope of the query item
TItem item

The item to find the nearest neighbour of
IItemDistance<Envelope, TItem> itemDist

A distance metric applicable to the items in this tree and the query item
Returns
Type Description
TItem

The nearest item in this tree or null if the tree is empty
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NearestNeighbour(Envelope, TItem, IItemDistance<Envelope, TItem>, int)

Finds up to k items in this tree which are the top k nearest neighbors to the given item, using itemDist as the distance metric. A Branch-and-Bound tree traversal algorithm is used to provide an efficient search. This method implements the KNN algorithm described in the following paper:

Roussopoulos, Nick, Stephen Kelley, and Fr�d�ric Vincent. "Nearest neighbor queries." ACM sigmod record. Vol. 24. No. 2. ACM, 1995.

The query item does not have to be contained in the tree, but it does have to be compatible with the itemDist distance metric.

If the tree size is smaller than k fewer items will be returned. If the tree is empty an array of size 0 is returned.
Declaration
public TItem[] NearestNeighbour(Envelope env, TItem item, IItemDistance<Envelope, TItem> itemDist, int k)
Parameters
Type Name Description
Envelope env

The envelope of the query item
TItem item

The item to find the nearest neighbours of
IItemDistance<Envelope, TItem> itemDist

A distance metric applicable to the items in this tree and the query item
int k

The maximum number of nearest items to search for
Returns
Type Description
TItem[]

An array of the nearest items found (with length between 0 and k)
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NearestNeighbour(IItemDistance<Envelope, TItem>)

Finds the two nearest items in the tree, using IItemDistance<T, TItem> as the distance metric. A Branch-and-Bound tree traversal algorithm is used to provide an efficient search.

If the tree is empty, the return value is null. If the tree contains only one item, the return value is a pair containing that item. If it is required to find only pairs of distinct items, the IItemDistance<T, TItem> function must be anti-reflexive.
Declaration
public TItem[] NearestNeighbour(IItemDistance<Envelope, TItem> itemDist)
Parameters
Type Name Description
IItemDistance<Envelope, TItem> itemDist

A distance metric applicable to the items in this tree
Returns
Type Description
TItem[]

The pair of the nearest items or null if the tree is empty
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NearestNeighbour(STRtree<TItem>, IItemDistance<Envelope, TItem>)

Finds the two nearest items from this tree and another tree, using IItemDistance<T, TItem> as the distance metric. A Branch-and-Bound tree traversal algorithm is used to provide an efficient search. The result value is a pair of items, the first from this tree and the second from the argument tree.

Declaration
public TItem[] NearestNeighbour(STRtree<TItem> tree, IItemDistance<Envelope, TItem> itemDist)
Parameters
Type Name Description
STRtree<TItem> tree

Another tree
IItemDistance<Envelope, TItem> itemDist

A distance metric applicable to the items in the trees
Returns
Type Description
TItem[]

The pair of the nearest items, one from each tree or null if no pair of distinct items can be found.
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Query(Envelope)

Returns items whose bounds intersect the given envelope.

Declaration
public IList<TItem> Query(Envelope searchEnv)
Parameters
Type Name Description
Envelope searchEnv
Returns
Type Description
IList<TItem>
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Query(Envelope, IItemVisitor<TItem>)

Returns items whose bounds intersect the given envelope.

Declaration
public void Query(Envelope searchEnv, IItemVisitor<TItem> visitor)
Parameters
Type Name Description
Envelope searchEnv
IItemVisitor<TItem> visitor
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Remove(Envelope, TItem)

Removes a single item from the tree.

Declaration
public bool Remove(Envelope itemEnv, TItem item)
Parameters
Type Name Description
Envelope itemEnv

The Envelope of the item to remove.
TItem item

The item to remove.
Returns
Type Description
bool

true if the item was found.
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VerticalSlices(IList<IBoundable<Envelope, TItem>>, int)

Declaration
protected IList<IBoundable<Envelope, TItem>>[] VerticalSlices(IList<IBoundable<Envelope, TItem>> childBoundables, int sliceCount)
Parameters
Type Name Description
IList<IBoundable<Envelope, TItem>> childBoundables

Must be sorted by the x-value of the envelope midpoints.
int sliceCount
Returns
Type Description
IList<IBoundable<Envelope, TItem>>[]

Implements