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Posted to dev@lucene.apache.org by "Srikanth Kallurkar (Commented) (JIRA)" <ji...@apache.org> on 2012/01/12 20:29:40 UTC
[jira] [Commented] (SOLR-2155) Geospatial search using geohash
prefixes
[ https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13185172#comment-13185172 ]
Srikanth Kallurkar commented on SOLR-2155:
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Hi David, Apologies for taking a long time to reply. I incorporated your suggestions and did see some speedup. I started with geohash length at 12 and got reasonable speed up for 8. T
But I am bit confused by (1) accuracy associated with length and (2) the query time operation in this patch.
(1) So, is the accuracy associated with how big/small an enclosing box is?
(2) The entire geohash field is loaded into memory at query time. Is this done because for the lat-lon comparisons, the patch cannot use lucene string matching mechanisms. Also, because the whole field is in memory, how are updates to the index handled. Meaning, if new lat-lons are added, do they get added to the in-memory geohashes.
Thanks,
Srikanth
> 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_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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