org.apache.lucene.spatial.prefix.tree

Class SpatialPrefixTree

java.lang.Object

org.apache.lucene.spatial.prefix.tree.SpatialPrefixTree

Direct Known Subclasses:

GeohashPrefixTree, NumberRangePrefixTree, QuadPrefixTree, S2PrefixTree

public abstract class SpatialPrefixTree
extends Object

A spatial Prefix Tree, or Trie, which decomposes shapes into prefixed strings at variable lengths corresponding to variable precision. Each string corresponds to a rectangular spatial region. This approach is also referred to "Grids", "Tiles", and "Spatial Tiers".

Implementations of this class should be thread-safe and immutable once initialized.

WARNING: This API is experimental and might change in incompatible ways in the next release.

Field Summary

Fields

Modifier and Type	Field and Description
protected org.locationtech.spatial4j.context.SpatialContext	ctx
protected int	maxLevels

Constructor Summary

Constructors

Constructor and Description
SpatialPrefixTree(org.locationtech.spatial4j.context.SpatialContext ctx, int maxLevels)

Method Summary

Modifier and Type	Method and Description
abstract double	getDistanceForLevel(int level) Given a cell having the specified level, returns the distance from opposite corners.
abstract int	getLevelForDistance(double dist) Returns the level of the largest grid in which its longest side is less than or equal to the provided distance (in degrees).
int	getMaxLevels()
org.locationtech.spatial4j.context.SpatialContext	getSpatialContext()
CellIterator	getTreeCellIterator(org.locationtech.spatial4j.shape.Shape shape, int detailLevel) Gets the intersecting cells for the specified shape, without exceeding detail level.
abstract Cell	getWorldCell() Returns the level 0 cell which encompasses all spatial data.
abstract Cell	readCell(BytesRef term, Cell scratch) This creates a new Cell (or re-using scratch if provided), initialized to the state as read by the bytes.
String	toString()

Methods inherited from class java.lang.Object

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

Field Detail

maxLevels

protected final int maxLevels

ctx

protected final org.locationtech.spatial4j.context.SpatialContext ctx

Constructor Detail

SpatialPrefixTree

public SpatialPrefixTree(org.locationtech.spatial4j.context.SpatialContext ctx,
                         int maxLevels)

Method Detail

getSpatialContext

public org.locationtech.spatial4j.context.SpatialContext getSpatialContext()

getMaxLevels

public int getMaxLevels()

toString

public String toString()

Overrides:

toString in class Object

getLevelForDistance

public abstract int getLevelForDistance(double dist)

Returns the level of the largest grid in which its longest side is less than or equal to the provided distance (in degrees). Consequently dist acts as an error epsilon declaring the amount of detail needed in the grid, such that you can get a grid with just the right amount of precision.

Parameters:

dist - >= 0

Returns:

level [1 to maxLevels]

getDistanceForLevel

public abstract double getDistanceForLevel(int level)

Given a cell having the specified level, returns the distance from opposite corners. Since this might vary depending on where the cell is, this method may over-estimate.

Parameters:

level - [1 to maxLevels]

Returns:

> 0

getWorldCell

public abstract Cell getWorldCell()

Returns the level 0 cell which encompasses all spatial data. Equivalent to readCell(BytesRef,Cell) with no bytes.

readCell

public abstract Cell readCell(BytesRef term,
                              Cell scratch)

This creates a new Cell (or re-using scratch if provided), initialized to the state as read by the bytes. Warning: An implementation may refer to the same byte array (no copy). If Cell.setLeaf() is subsequently called, it would then modify these bytes.

getTreeCellIterator

public CellIterator getTreeCellIterator(org.locationtech.spatial4j.shape.Shape shape,
                                        int detailLevel)

Gets the intersecting cells for the specified shape, without exceeding detail level. If a cell is within the query shape then it's marked as a leaf and none of its children are added. For cells at detailLevel, they are marked as leaves too, unless it's a point.

IMPORTANT: Cells returned from the iterator can be re-used for cells at the same level. So you can't simply iterate to subsequent cells and still refer to the former cell nor the bytes returned from the former cell, unless you know the former cell is a parent.

Parameters:

shape - the shape; possibly null but the caller should liberally call remove() if so.

detailLevel - the maximum detail level to get cells for

Returns:

the matching cells