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From "Robert Muir (JIRA)" <>
Subject [jira] Commented: (SOLR-2155) Geospatial search using geohash prefixes
Date Wed, 13 Oct 2010 13:52:32 GMT


Robert Muir commented on SOLR-2155:

One area that I know nothing about is how scoring/sorting actually works within Lucene. For
the work here I wasn't in need of that but many people clearly want that. In your opinion
Rob, is there any opportunity for geo sorting/relevancy code to take advantage of any efficiencies
done here or are they completely unrelated?

Thats a good question, I'm not sure this stuff will help with that. But there is also a lot
of people who like you, don't need/want to integrate it into scoring and maybe just want to
filter on distance really fast, and score based on something else.

I'm not a spatial guy and don't understand the spatial goings-on, but it seems like maybe
people who want to do relevance based on distance could achieve that some other way and use
the trie value to just have a really fast bounding "box" filter.

maybe they use a solr function query or however this is done but the filter would speed it
up tremendously, of course with some loss of precision, but this is search, its not like the
textual component has perfect precision, and a lot of people arent going across meridians
or the earth's poles or anything.

> Geospatial search using geohash prefixes
> ----------------------------------------
>                 Key: SOLR-2155
>                 URL:
>             Project: Solr
>          Issue Type: Improvement
>            Reporter: David Smiley
>         Attachments: GeoHashPrefixFilter.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 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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