Gilad Barkai created LUCENE-5271:
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Summary: 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
Priority: Minor
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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