Geospatial search using geohash prefixes
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Key: SOLR-2155
URL: https://issues.apache.org/jira/browse/SOLR-2155
Project: Solr
Issue Type: Improvement
Reporter: David Smiley
There currently isn't a solution in Solr for doing geospatial filtering on
documents that have a variable number of points. This scenario occurs when
there is location extraction (i.e. via a "gazateer") occurring on free text.
None, one, or many geospatial locations might be extracted from any given
document and users want to limit their search results to those occurring in a
user-specified area.
I've implemented this by furthering the GeoHash based work in Lucene/Solr with
a geohash prefix based filter. A geohash refers to a lat-lon box on the earth.
Each successive character added further subdivides the box into a 4x8 (or 8x4
depending on the even/odd length of the geohash) grid. The first step in this
scheme is figuring out which geohash grid squares cover the user's search
query. I've added various extra methods to GeoHashUtils (and added tests) to
assist in this purpose. The next step is an actual Lucene Filter,
GeoHashPrefixFilter, that uses these geohash prefixes in TermsEnum.seek() to
skip to relevant grid squares in the index. Once a matching geohash grid is
found, the points therein are compared against the user's query to see if it
matches. I created an abstraction GeoShape extended by subclasses named
PointDistance... and CartesianBox.... to support different queried shapes so
that the filter need not care about these details.
This work was presented at LuceneRevolution in Boston on October 8th.
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