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From "David Smiley (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-2155) Geospatial search using geohash prefixes
Date Mon, 17 Oct 2011 17:00:11 GMT

    [ https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13129002#comment-13129002
] 

David Smiley commented on SOLR-2155:
------------------------------------

Oliver: Your scenario is interesting but I wouldn't recommend spatial for that. A key part
of spatial is the use of a numerical range. In your case there are discrete values.  Instead,
I recommend you experiment with phrase queries, and if you are expert in Lucene then span
queries.  As a toy hack example, imagine indexing each of these values in the form "senior
developer java" (3 words, one for each part). We assume each value tokenizes as one token.
 Then search for "the developer java" in which "the" was substituted as a kind of wildcard
for the first position to find java developers in all levels of experience. "The" is a stopword
and in effect creates a wildcard placeholder.  If you search the solr-user list then you will
see information on this topic.  I've solved this problem in a different more difficult way
because my values were not single tokens, but based on the example you present, the solution
I present here isn't bad.  If you want to discuss this further I recommend the solr-user list.
                
> Geospatial search using geohash prefixes
> ----------------------------------------
>
>                 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_GeoHashPrefixFilter_with_sorting_no_poly.patch, SOLR.2155.p3.patch, SOLR.2155.p3tests.patch,
Solr2155-1.0.2-project.zip, Solr2155-1.0.3-project.zip, Solr2155-for-1.0.2-3.x-port.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.

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