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https://issues.apache.org/jira/browse/LUCENE-5271?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13905917#comment-13905917
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David Smiley commented on LUCENE-5271:
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Cool!
> A slightly more accurate SloppyMath distance
> --------------------------------------------
>
> Key: LUCENE-5271
> URL: https://issues.apache.org/jira/browse/LUCENE-5271
> Project: Lucene - Core
> Issue Type: Improvement
> Components: modules/other
> Reporter: Gilad Barkai
> Assignee: Ryan Ernst
> Priority: Minor
> Fix For: 4.7, 5.0
>
> Attachments: LUCENE-5271.patch, LUCENE-5271.patch, LUCENE-5271.patch
>
>
> SloppyMath, intriduced in LUCENE-5258, uses earth's avg. (according to WGS84)
> ellipsoid radius as an approximation for computing the "spherical" distance.
> (The TO_KILOMETERS constant).
> While this is pretty accurate for long distances (latitude wise) this may
> introduce some small errors while computing distances close to the equator
> (as the earth radius there is larger than the avg.)
> A more accurate approximation would be taking the avg. earth radius at the
> source and destination points. But computing an ellipsoid radius at any given
> point is a heavy function, and this distance should be used in a scoring
> function.. So two optimizations are optional -
> * Pre-compute a table with an earth radius per latitude (the longitude does
> not affect the radius)
> * Instead of using two point radius avg, figure out the avg. latitude
> (exactly between the src and dst points) and get its radius.
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