The Spatial-Extras Module for Apache Lucene
    The spatial-extras module, new to Lucene 6.5, is the new home for the original
    lucene spatial module.
    The principle interface to this module is a SpatialStrategy
    which encapsulates an approach to indexing and searching
    based on shapes.  Different Strategies have different features and
    performance profiles, which are documented at each Strategy implementation
    class level.
  
For some sample code showing how to use the API, see SpatialExample.java in the tests.
The spatial-extras module uses Spatial4j heavily. Spatial4j is an ASL licensed library with these capabilities:
- Provides shape implementations, namely point, rectangle, and circle. Both geospatial contexts and plain 2D Euclidean/Cartesian contexts are supported. With an additional dependency, it adds polygon and other geometry shape support via integration with JTS Topology Suite. This includes dateline wrap support.
- Shape parsing and serialization, including Well-Known Text (WKT) (via JTS).
- Distance and other spatial related math calculations.
    Historical note: The new spatial-extras module was once known as
    Lucene Spatial Playground (LSP) as an external project.  In ~March 2012, LSP
    split into the spatial module as part of Lucene and Spatial4j externally. A
    large chunk of the LSP implementation originated as SOLR-2155 which uses
    trie/prefix-tree algorithms with a geohash encoding.  That approach is
    implemented in RecursivePrefixTreeStrategy
    today.
  
| Package | Description | 
|---|---|
| org.apache.lucene.spatial | Lucene advanced spatial search | 
| org.apache.lucene.spatial.bbox | Bounding Box Spatial Strategy | 
| org.apache.lucene.spatial.composite | Composite strategies. | 
| org.apache.lucene.spatial.prefix | Prefix Tree Strategy. | 
| org.apache.lucene.spatial.prefix.tree | This package is about SpatialPrefixTree and any supporting classes. | 
| org.apache.lucene.spatial.query | Spatial Query options useful for client side requests | 
| org.apache.lucene.spatial.serialized | Strategies that serialize the shape (non-indexed). | 
| org.apache.lucene.spatial.spatial4j | Spatial4j stuff that ideally belongs in Spatial4j (isn't related to Lucene). | 
| org.apache.lucene.spatial.util | Advanced spatial utilities. | 
| org.apache.lucene.spatial.vector | Spatial strategy that uses two fields. |