An overview of spatial/geospatial developments on Lucene and Solr during 2015 (thru Oct). Presented at Lucene/Solr Revolution 2015 in Austin.

1. O C T O B E R 1 3 - 1 6 , 2 0 1 6 • A U S T I N , T X

2. Lucene/Solr Spatial in 2015
David Smiley
Search Engineer/Consultant (Freelance)

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About David Smiley
Freelance Search Developer/Consultant
Expert Lucene/Solr development skills,
advise (consulting), training
Java, spatial, and full-stack experience
Apache Lucene/Solr committer & PMC member
Primary author of “Apache Solr Enterprise Search Server”

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More Spatial Contributors!
Spatial4j Lucene Solr
David Smiley ✔️ ✔️ ✔️
Ryan McKinley ✔️
Justin Deoliveira ✔️
Mike McCandless ✔️
Nick Knize ✔️
Karl Wright ✔️
Ishan Chattopadhyaya ✔️

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Agenda
New Features / Capabilities
New Approaches
Improvements
Pending

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Topic: New Features
Heatmaps / grid faceting — Lucene, Solr
Surface-of-sphere shapes (Geo3d) — Lucene
Accurate indexed geometries — Lucene, Solr
GeoJSON read/write — Spatial4j

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Heatmaps: Spatial Grid Faceting
Spatial density summary grid faceting,
also useful for point-plotting search results
Usually rendered with a gradient radius
Lucene & Solr APIs
Scalable & fast usually…
v5.2

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Heatmaps Under the Hood
Requires a PrefixTreeStrategy Lucene field — grid based
Algorithm enumerates the underlying cell/terms and accumulates
the counter in a corresponding grid
Conceptually facet.method=enum for spatial
Works on non-point indexed shapes too
Complexity: O(cells * cellDepthFactor) not O(docs)
No/low memory; mainly the grid of integers
Solr will distribute to shards and merge
Could be faster still; a BFS (vs DFS) layout would be perfect

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Solr Heatmap Faceting
On an RPT field
(SpatialRecursivePrefixTreeFieldType)
prefixTree=“packedQuad”
Query:
/select?facet=true
&facet.heatmap=geo_rpt
&facet.heatmap.geom=
["-180 -90" TO "180 90”]
facet.heatmap.format=ints2D or png
// Normal Solr response...
"facet_counts":{
... // facet response fields
"facet_heatmaps":{
"loc_srpt":[
"gridLevel",2,
"columns",32,
"rows",32,
"minX",-180.0,
"maxX",180.0,
"minY",-90.0,
"maxY",90.0,
"counts_ints2D", [null, null, [0, 0, ... ]]
...

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Solr Heatmap Resources
Solr Ref guide:
https://cwiki.apache.org/confluence/display/solr/Spatial+Search
Jack Reed’s Tutorial: http://www.jack-reed.com/2015/06/29/visualizing-10-
million-geonames-with-leaflet-solr-heatmap-facets.html
Live Demo: http://worldwidegeoweb.com
Open-source JavaScript Solr Heatmap Libraries
https://github.com/spacemansteve/SolrHeatmapLayer
https://github.com/mejackreed/leaflet-solr-heatmap
https://github.com/voyagersearch/leaflet-solr-heatmap

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Geo3D: Shapes on the Surface of a Sphere
… or Ellipsoid of configurable axis
Not a general 3D space geometry lib
Internally uses geocentric X, Y, Z coordinates (hence 3D) with
3D planar geometry mathematics
Shapes: Point, Lat-Lon Rect, Circle, Polygons, Path (LineString)
with optional buffer
Distance computations: Arc (angular or surface), Linear (straight-
line), Normal

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All 2D Maps of the Earth Distort Straight Lines
A straight bird-flies
path from
Anchorage to
Miami doesn’t
actually cross the
ocean!

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Geo3D, continued…
Benefits
Inherently more accurate than 2D projected spatial
especially for big shapes or near poles
Many computations are fast; no expensive trigonometry
An alternative to JTS without the LGPL license (still)
Has own Lucene module (spatial3d), thus jar file
Maven groupId: org.apache.lucene, artifact: lucene-spatial3d
No Solr integration yet; pending more Spatial4j integration

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Index & Search Geo3D Geometries
Spatial4j Geo3dShape
wrapper with RPT
In Lucene-spatial for now
Index Geo3d shapes
Limited to grid accuracy
Query by Geo3d shape
Limited distance sort
Heatmaps
Geo3DPointField &
PointInGeo3DShapeQuery
Based on a 3D BKD index
In spatial3d module
Index points-only
No multi-valued
Query by Geo3d shape
No distance sort
Leaner & faster than RPT
v5.4v5.2

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RPT/SpatialPrefixTrees and Accuracy
RecursivePrefixTree (RPT) uses Lucene’s index as a PrefixTree
Thus represents shapes as grid cells of varying precision by
prefix
Example, a point shape:
D, DR, DRT, DRT2, DRT2Y
More accuracy scales
Example, a polygon shape:
Too many to list… 508 cells
More accuracy does NOT scale

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Combining RPT with Serialized Geometry
RPT (RecursivePrefixTreeStrategy) is the grid index (inaccurate)
SDV (SerializedDVStrategy) stores serialized geometry (accurate)
RPT + SDV → CompositeSpatialStrategy
Accuracy & speed & smaller indexes
Optimized intersects predicate avoids some geometry checks
> 80% faster intersects queries, 75% smaller index
Solr adapter: RptWithGeometrySpatialField
Compatible with the Heatmaps feature
Includes a shape cache (per-segment); configurable
v5.2

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Topic: New Approaches
Lucene
BKD Tree Indexes
GeoPointField

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BKD Tree Indexes
New numeric/spatial index approach with own file format
Not based on Lucene Terms index
https://www.cs.duke.edu/~pankaj/publications/papers/bkd-sstd.pdf
Much faster and compact than Trie/PrefixTree based indexes
Wither term auto-prefixing? LUCENE-5879
Indexed point-data only; multi-valued mostly
Intersects predicate only
Filtering only (no distance or other scoring)
Multiple implementations… (next slide)
Neat visualization
https://youtu.be/x9WnzOvsGKs

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Multiple BKD Implementations
Multiple implementations of the same BKD concept:
(1D) RangeTreeDocValuesFormat
(2D) BKDPointField & BKD…Query
(3D) Geo3DPointField & PointInGeo3DShapeQuery
(ND) LUCENE-6825 (to Lucene-core) in-progress
1D,2D,3D Implementations are either in lucene-sandbox or
lucene-spatial3d for now
No Lucene-spatial module SpatialStrategy wrappers yet
thus no Spatial4j Shape integration nor Solr integration yet

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BKD 1D: RangeTree
Efficient range search on single/multi-valued numbers or terms
Could be used for numbers, dates, IPV6 bytes, …
Alternatives: Normal number fields (trie), DateRangeField (RPT)
Would love to see a benchmark!
How-To:
RangeTreeDocValuesFormat
Numbers: SortedNumericDocValuesField with
NumericRangeTreeQuery
Bytes: SortedSetDocValuesField with SortedSetRangeTreeQuery
v5.3

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BKD 2D: BKDPointField
Efficient 2D geospatial point index
Alternative to RPT or GeoPointField
5.7x faster than RPT w/ GeoHash. Smaller indexes.
How-To:
Use BKDPointField (requires BKDTreeDocValuesFormat)
Query:
BKDPointInBBoxQuery
BKDPointInPolygonQuery
point-radius (circle) — in-progress LUCENE-6698
v5.3

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GeoPointField
2D geospatial point field
Indexed point-only data, single/multi-valued
Spatial 2D Trie/PrefixTree terms index
But not affiliated with Lucene-spatial SpatialPrefixTree/RPT
Configurable 2x grid size (defaults to 512)
Compact bit interleaved Z-order encoding
Re-uses much of Lucene’s numeric precisionStep &
MultiTermQuery logic
2-phase grid/postings then doc-values algorithm
v5.3

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…continued
Has no affiliation with Spatial4j, RPT, JTS, or SpatialStrategy
No Heatmaps, No custom Shape implementations
No Solr support yet
No dependencies
Easy to use compared to RPT; simpler internally too
How-To:
doc.add(new GeoPointField(name, lon, lat, Store.YES))
GeoPointDistanceQuery (sphere only) or GeoPointInBBoxQuery
or GeoPointInPolygonQuery. …DistanceRangeQuery pending

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Topic: Improvements
Spatial4j
Minimal longitude bounding-box algorithm
Lucene (PrefixTree / RPT indexing)
Leaner & faster non-point indexes
New PackedQuadPrefixTree
Solr
Distance units: Kilometers/Miles/Degrees
Nicer ST_* spatial query parsers (almost done)

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Topic: Some Pending Spatial TODOs
Spatial4j
Geo3D integration — a JTS
alternative
Lucene
FlexPrefixTree — LUCENE-
4922
Multi-dimensional BKD —
LUCENE-6825
SpatialStrategy adapters for
GeoPointField, etc.
Solr
Better spatial Solr
QParsers — SOLR-4242
GeoJSON parsing
More FieldType adapters
for latest Lucene spatial
DateRangeField faceting
Nearest-neighbor search
Well, 2015 isn’t over yet.
:-)

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That’s all for now; thanks for coming!
Need Lucene/Solr guidance or custom development?
Contact me!
Email: dsmiley@apache.org
LinkedIn: http://www.linkedin.com/in/davidwsmiley
G+: +DavidSmiley
Twitter: @DavidWSmiley