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From "Lance Norskog (JIRA)" <>
Subject [jira] Commented: (SOLR-2155) Geospatial search using geohash prefixes
Date Sat, 23 Oct 2010 00:29:19 GMT


Lance Norskog commented on SOLR-2155:

I've reread the patch a few times and I understand it better now, and yes there should be
no equator/prime meridian problems. I retract any overt or implied criticism.

bq. First of all, I'm re-using the existing geohash field support in Solr which indexes the
lat-lons as actual geohashes (i.e. the character representation), not in a bitwise fashion.
But that doesn't really matter - it would be a worthwhile optimization to index them in that
fashion as it would be more compact.

Using the canonical geohash gives facet values that can be copy&pasted with other software.
Thinking again, this is a great feature. Would it be worth optimizing geohash with a Trie
version?  Trie fields (can be made to) show up correctly in facets.

And thank you for the word [gazateer||.

About unit tests: I've stumbled so many times with floating point that I only trust real-world
data. A good unit test would be indexing a [gazateer||
of world data and randomly comparing points. OpenStreetMaps or Wikipedia locations for example.

> Geospatial search using geohash prefixes
> ----------------------------------------
>                 Key: SOLR-2155
>                 URL:
>             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 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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