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https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920536#action_12920536
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David Smiley commented on SOLR-2155:
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Yes, absolutely Rob. I went with geohashes because it was a straight-forward
implementation to prove out the concept. It appears my patch is the first of
its kind for Lucene/Solr. For doing a more efficient Morton representation, I
have already looked at the work going on at javageomodel:
http://code.google.com/p/javageomodel/ which was built for use with Google
BigTable. The code there is largely pure java, keep in mind. It's the same
concept but it uses a dictionary of size 16 (representable by 4 bits) which
results in cleaner algorithms than geohashes' 5-bit dictionary which has some
even/odd rules to it which are awkward. But yes, it would be more efficient to
store the actual intended bits, not characters.
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?
(I meant to track you down at LuceneRevolution to say hi but I missed the
opportunity.)
> 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
>
>
> 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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