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From "Bill Bell (JIRA)" <j...@apache.org>
Subject [jira] Commented: (SOLR-2155) Geospatial search using geohash prefixes
Date Sun, 13 Feb 2011 02:19:57 GMT

    [ https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12994010#comment-12994010
] 

Bill Bell commented on SOLR-2155:
---------------------------------

David,

Who is the committer assigned to this ticket?

I agree that I need to find a way to get at the MultiValue fields for LatLon and GeoHash.
I will start working on trying to get that to work. Probably first with GeoHash since you
already deal with multiValue (gazateer). LatLon does not handle multi values yet. Based on
your patch it seems like I can do.

I like the parallel idea too.

I finally see your point. The use case is when you do a geodist() without a {!geofilt}. This
would be very slow since you would be looping through a large result set. However if you were
to throw away far points, you would need to know the "d=" parameter (making that mandatory).
The current implementation does not require "radius". I also think your geohash combined with
geomultidist() is awesome. We just need to try to make it faster.

I will continue working on this - since my client needs it now. Just tell me what I need to
do, what you recommend, use cases, etc. If we can get a committer involved, it might get included
in 4.0.

Bill



> 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
>         Attachments: GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch,
SOLR.2155.p2.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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