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From "Sandeep Tucknat (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SOLR-2155) Geospatial search using geohash prefixes
Date Fri, 01 Mar 2013 16:33:13 GMT

    [ https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13590679#comment-13590679
] 

Sandeep Tucknat commented on SOLR-2155:
---------------------------------------

First of all, thanks for the prompt response! It feels good to see you are supporting the
approach we took in the interim :) I was just thinking that in order to do the ranking, the
filter has to go through all the values of the field and it shouldn't be hard to persist this
information and return to the client. We'll be waiting for that optimization to come through!
Many thanks! let me know if I can help in any way (3 weeks in spatial or solr).
                
> 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: David Smiley
>         Attachments: GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch,
Solr2155-1.0.2-project.zip, Solr2155-1.0.3-project.zip, Solr2155-1.0.4-project.zip, Solr2155-for-1.0.2-3.x-port.patch,
SOLR-2155_GeoHashPrefixFilter_with_sorting_no_poly.patch, SOLR.2155.p3.patch, SOLR.2155.p3tests.patch
>
>
> {panel:title=NOTICE} The status of this issue is a plugin for Solr 3.x located here:
https://github.com/dsmiley/SOLR-2155.  Look at the introductory readme and download the plugin
.jar file.  Lucene 4's new spatial module is largely based on this code.  The Solr 4 glue
for it should come very soon but as of this writing it's hosted temporarily at https://github.com/spatial4j.
 For more information on using SOLR-2155 with Solr 3, see http://wiki.apache.org/solr/SpatialSearch#SOLR-2155
 This JIRA issue is closed because it won't be committed in its current form.
> {panel}
> 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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