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 Assignee: Grant Ingersoll Attachments: GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch,
GeoHashPrefixFilter.patch, SOLR.2155.p3.patch, SOLR.2155.p3tests.patch

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.