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