Package org.apache.lucene.spatial.prefix

Class 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(org.locationtech.spatial4j.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(org.locationtech.spatial4j.shape.Point,double) 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.

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

    • Field Detail

      • defaultFieldValuesArrayLen

        protected int defaultFieldValuesArrayLen

      • distErrPct

        protected double distErrPct

      • pointsOnly

        protected boolean pointsOnly

      • FIELD_TYPE

        public static final FieldType FIELD_TYPE

    • Method Detail

      • 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()

      • isPointsOnly

        public boolean isPointsOnly()

      • setPointsOnly

        public void setPointsOnly​(boolean pointsOnly)
        True if only indexed points shall be supported. There are no "leafs" in such a case, except those at maximum precision.

      • createIndexableFields

        public Field[] createIndexableFields​(org.locationtech.spatial4j.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​(org.locationtech.spatial4j.shape.Shape shape,
                                     int detailLevel)

      • createCellIteratorToIndex

        protected Iterator<Cell> createCellIteratorToIndex​(org.locationtech.spatial4j.shape.Shape shape,
                                                   int detailLevel,
                                                   Iterator<Cell> reuse)

      • makeDistanceValueSource

        public DoubleValuesSource makeDistanceValueSource​(org.locationtech.spatial4j.shape.Point queryPoint,
                                                  double multiplier)
        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. The result is multiplied by multiplier, which conveniently is used to get the desired units.
        Specified by:
        makeDistanceValueSource in class SpatialStrategy

      • isPointShape

        protected boolean isPointShape​(org.locationtech.spatial4j.shape.Shape shape)
        Returns true if the shape is a Point. For custom spatial contexts, it may make sense to have certain other shapes return true.
        WARNING: This API is experimental and might change in incompatible ways in the next release.