Nicholas Knize created LUCENE-7110:
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Summary: Add Shape Support to BKD (extend to an R*/X-Tree data
structure)
Key: LUCENE-7110
URL: https://issues.apache.org/jira/browse/LUCENE-7110
Project: Lucene - Core
Issue Type: New Feature
Reporter: Nicholas Knize
I've been tinkering with this off and on for a while and its showing some
promise so I'm going to open an issue to (eventually) add this feature to
either a 6.x or (more likely) a 7.x release.
R*/X-Tree is a data structure designed to support Shapes (2D, 3D, nD) where,
like the internal node, the key for each leaf node is the Minimum Bounding
Range (MBR - sometimes "incorrectly" referred to as Minimum Bounding Rectangle)
of the shape. Inserting a shape then boils down to the best way of optimizing
the tree structure. This optimization is driven by a set of criteria for
choosing the appropriate internal key (e.g., minimizing overlap between
siblings, maximizing "squareness", minimizing area, maximizing space usage).
Query is then (a bit oversimplified) a two-phase process:
* recurse each branch that overlaps with the MBR of the query shape
* compute the relation with the leaf node(s) - in higher dimensions (3+) this
becomes an increasingly difficult computational geometry problem
The current BKD implementation is a special simplified case of an R*/X tree
where, for Point data, it is always guaranteed there will be no overlap between
sibling nodes (because you're using the point data as the keys). By exploiting
this property the tree algorithms (split, merge, etc) are relatively cheap
(hence their performance boost over postings based numerics). By modifying the
key data, and extending the tree generation algorithms BKD logic can be
extended to support Shape data using the MBR as the Key and modifying split and
merge based on the criteria needed for optimizing a shape-based data structure.
The initial implementation (based on limitations of the GeoAPI) will support 2D
shapes only. Once the GeoAPI can performantly handle 3D shapes the change is
relatively trivial to add the third dimension to the tree generation code.
Like everything else, this feature will be created in sandbox and, once mature,
will graduate to lucene-spatial.
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