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From Erick Erickson <erickerick...@gmail.com>
Subject Re: [jira] [Commented] (SOLR-2155) Geospatial search using geohash prefixes
Date Wed, 17 Oct 2012 12:08:23 GMT
Robert:

It's much better to ask usage questions like this on the user's list
rather than in a
comment on a JIRA, the user's list gets seen by a much wider audience. See
the solr-user section here: http://lucene.apache.org/solr/discussion.html

Quick answers:
1> you're better off chunking things up. But beware the "deep paging"
problem, as
     you go farther and farther into the list, response will slow down.
2> top N is indeed based on score, see the scoring algorithm in the
Similarity (Lucene)
     class. And it's just the top &rows documents. Their scores could
be > 0.99999 or
     < 0.0000001, just the top N. If two docs have the exact same
score, the tie is
     broken by the internal Lucene doc ID so the results are consistent.

Why do you want to return all the docs anyway? Some kind of dump?
Perhaps there's
a better way do do what you want.

But again, please move the discussion over to the user's list.

Best
Erick

On Wed, Oct 17, 2012 at 2:20 AM, Robert Tseng (JIRA) <jira@apache.org> wrote:
>
>     [ https://issues.apache.org/jira/browse/SOLR-2155?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13477653#comment-13477653
]
>
> Robert Tseng commented on SOLR-2155:
> ------------------------------------
>
> Hi All,
>
> New to Solr here!  I have a question for you all on gh_geofilt.  My document has rows
of path, think of KML lineString, of which I want to do bounding box check which of them fall
within a box.  Each row basically has an id field and a multivalued field describing the line
with multiple points.
>
> What I want returned is all lines that fall within but I read Solr is not very good,
yet, in returning large number of hits.  Hence the row params to limit result to top N rows.
 My two questions are:
>
> 1. If want to retrieve all rows, do I query twice from solrj.  Once to get number of
hits so I can set the number of rows that grabs all row in a second call? Or two I should
chunk up the query call using the start params as an offset?
>
> 2. If it's only returning top N, is it based on score?  What is considered high score?
A row with most number of hits in the box? Cloest to the center?
>
>> 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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