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From "David Smiley (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SOLR-2155) Geospatial search using geohash prefixes
Date Thu, 31 Mar 2011 22:09:05 GMT

     [ https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

David Smiley updated SOLR-2155:
-------------------------------

    Attachment: SOLR-2155_GeoHashPrefixFilter_with_sorting_no_poly.patch

Attached is a new patch. The highlights are:
 * Requires the latest Solr trunk -- probably anything in the last few months: If this is
ultimately going to get committed then this needed to happen.  There are only some slight
differences so if you really need an earlier trunk then I'm sure you'll figure it out.
 * Adds support for sorting, including multi-value: Use the existing geodist() function query
with a lat-lon constant and a reference to your geohash based field. Note that this works
by loading all points from the field into memory, resolving each underlying full-length geohash
into the lat & lon into a data structure which is a List<Point2D>[].  This is improved
over Bill's patch, surely, but it could use some optimization.  It's not optimized for the
single-value case either; that's a definite TODO.
 * Polygon/WKT features have been omitted due to LGPL licensing concerns of JTS. I've left
hooks for their implementation to make adding on this capability that already existed easy.
You'll easily figure it out if you are so inclined.  I might ad this as a patch shortly (not
to be committed) when I get some time; but longer term it will re-surface under a separate
project.  Don't worry; it'll be painless to use if you need it.
 * This might be controversial but as part of this patch, I removed the ghhsin() and geohash()
function queries. Their presence was confusing; I simply don't see what point there is too
them now that this patch fleshes out the geohash capability.
 * I decided to pre-register my "SpatialGeoHashFilterQParser" as "geohashfilt", instead of
requiring you to do so in solrconfig.xml.  You could use "geofilt" for point-radius queries
but I prefer this one since I can specify the bbox explicitly.

There are a few slight changes to GeoHashPrefixFilter that crept in from unfinished work (notably
tying sorting to filtering in an efficient way) but it is harmless.

Bill, thanks for kick-starting the multi-value sorting. I re-used most of your code.

> 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: Grant Ingersoll
>         Attachments: GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch, GeoHashPrefixFilter.patch,
SOLR-2155_GeoHashPrefixFilter_with_sorting_no_poly.patch, SOLR.2155.p3.patch, SOLR.2155.p3tests.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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