org.apache.lucene.spatial.prefix
Class PrefixTreeStrategy

java.lang.Object
  org.apache.lucene.spatial.SpatialStrategy
      org.apache.lucene.spatial.prefix.PrefixTreeStrategy

Direct Known Subclasses:

RecursivePrefixTreeStrategy, TermQueryPrefixTreeStrategy

public abstract class PrefixTreeStrategy
extends SpatialStrategy

An abstract SpatialStrategy based on SpatialPrefixTree. The two subclasses are RecursivePrefixTreeStrategy and TermQueryPrefixTreeStrategy. This strategy is most effective as a fast approximate spatial search filter.

Characteristics:

• Can index any shape; however only RecursivePrefixTreeStrategy can effectively search non-point shapes.
• Can index a variable number of shapes per field value. This strategy can do it via multiple calls to createIndexableFields(com.spatial4j.core.shape.Shape) for a document or by giving it some sort of Shape aggregate (e.g. JTS WKT MultiPoint). The shape's boundary is approximated to a grid precision.
• Can query with any shape. The shape's boundary is approximated to a grid precision.
• Only SpatialOperation.Intersects is supported. If only points are indexed then this is effectively equivalent to IsWithin.
• The strategy supports makeDistanceValueSource(com.spatial4j.core.shape.Point) even for multi-valued data, so long as the indexed data is all points; the behavior is undefined otherwise. However, it will likely be removed in the future in lieu of using another strategy with a more scalable implementation. Use of this call is the only circumstance in which a cache is used. The cache is simple but as such it doesn't scale to large numbers of points nor is it real-time-search friendly.

Implementation:

The SpatialPrefixTree does most of the work, for example returning a list of terms representing grids of various sizes for a supplied shape. An important configuration item is setDistErrPct(double) which balances shape precision against scalability. See those javadocs.

NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

Field Summary

protected int	defaultFieldValuesArrayLen
protected double	distErrPct
static FieldType	FIELD_TYPE
protected SpatialPrefixTree	grid
protected boolean	simplifyIndexedCells

Fields inherited from class org.apache.lucene.spatial.SpatialStrategy

ctx

Constructor Summary

PrefixTreeStrategy(SpatialPrefixTree grid, String fieldName, boolean simplifyIndexedCells)

Method Summary

Field[]	createIndexableFields(com.spatial4j.core.shape.Shape shape) Returns the IndexableField(s) from the shape that are to be added to the Document.
Field[]	createIndexableFields(com.spatial4j.core.shape.Shape shape, double distErr)
double	getDistErrPct()
SpatialPrefixTree	getGrid()
ValueSource	makeDistanceValueSource(com.spatial4j.core.shape.Point queryPoint) Make a ValueSource returning the distance between the center of the indexed shape and queryPoint.
void	setDefaultFieldValuesArrayLen(int defaultFieldValuesArrayLen) A memory hint used by makeDistanceValueSource(com.spatial4j.core.shape.Point) for how big the initial size of each Document's array should be.
void	setDistErrPct(double distErrPct) The default measure of shape precision affecting shapes at index and query times.

Methods inherited from class org.apache.lucene.spatial.SpatialStrategy

getFieldName, getSpatialContext, makeFilter, makeQuery, makeRecipDistanceValueSource, toString

Methods inherited from class java.lang.Object

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

Field Detail

grid

protected final SpatialPrefixTree grid

simplifyIndexedCells

protected final boolean simplifyIndexedCells

defaultFieldValuesArrayLen

protected int defaultFieldValuesArrayLen

distErrPct

protected double distErrPct

FIELD_TYPE

public static final FieldType FIELD_TYPE

Constructor Detail

PrefixTreeStrategy

public PrefixTreeStrategy(SpatialPrefixTree grid,
                          String fieldName,
                          boolean simplifyIndexedCells)

Method Detail

setDefaultFieldValuesArrayLen

public void setDefaultFieldValuesArrayLen(int defaultFieldValuesArrayLen)

A memory hint used by makeDistanceValueSource(com.spatial4j.core.shape.Point) for how big the initial size of each Document's array should be. The default is 2. Set this to slightly more than the default expected number of points per document.

getDistErrPct

public double getDistErrPct()

setDistErrPct

public void setDistErrPct(double distErrPct)

The default measure of shape precision affecting shapes at index and query times. Points don't use this as they are always indexed at the configured maximum precision (SpatialPrefixTree.getMaxLevels()); this applies to all other shapes. Specific shapes at index and query time can use something different than this default value. If you don't set a default then the default is SpatialArgs.DEFAULT_DISTERRPCT -- 2.5%.

See Also:

SpatialArgs.getDistErrPct()

createIndexableFields

public Field[] createIndexableFields(com.spatial4j.core.shape.Shape shape)

Description copied from class: SpatialStrategy

Returns the IndexableField(s) from the shape that are to be added to the Document. These fields are expected to be marked as indexed and not stored.

Note: If you want to store the shape as a string for retrieval in search results, you could add it like this:

document.add(new StoredField(fieldName,ctx.toString(shape)));

The particular string representation used doesn't matter to the Strategy since it doesn't use it.

Specified by:

createIndexableFields in class SpatialStrategy

Returns:

Not null nor will it have null elements.

createIndexableFields

public Field[] createIndexableFields(com.spatial4j.core.shape.Shape shape,
                                     double distErr)

makeDistanceValueSource

public ValueSource makeDistanceValueSource(com.spatial4j.core.shape.Point queryPoint)

Description copied from class: SpatialStrategy

Make a ValueSource returning the distance between the center of the indexed shape and queryPoint. If there are multiple indexed shapes then the closest one is chosen.

Specified by:

makeDistanceValueSource in class SpatialStrategy

getGrid

public SpatialPrefixTree getGrid()