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https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13590706#comment-13590706
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David Smiley commented on SOLR-2155:
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bq. 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
It doesn't; this is a common misconception! It does *not* calculate the
distance between every indexed matched point and the center point of a circle
query shape. If it did, it wouldn't be so fast :-) If you want an
implementation like that then look at LatLonType which is a brute force
algorithm and hence is not as scalable, and doesn't support multi-value either.
To try and help explain how this can possibly be, understand that there are
large grid cells that fit within the query shape and for these large grid
cells, the index knows which documents are all in that grid cell and so it
simply matches those documents without knowing or calculating more precisely
where those underlying points actually are. So it's not like the filter code
has all this information you want and simply isn't exposing it to you. I need
to drive this point home at my next conference presentation at Lucene/Solr
Revolution 2013 in May (San Diego CA).
> 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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