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From "David Smiley (JIRA)" <j...@apache.org>
Subject [jira] Created: (SOLR-2155) Geospatial search using geohash prefixes
Date Wed, 13 Oct 2010 04:18:32 GMT
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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