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https://issues.apache.org/jira/browse/LUCENE-3814?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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David Smiley reassigned LUCENE-3814:
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Assignee: David Smiley
> Manhattan distance function is incorrect, not absolute distance between
> coordinates
> -----------------------------------------------------------------------------------
>
> Key: LUCENE-3814
> URL: https://issues.apache.org/jira/browse/LUCENE-3814
> Project: Lucene - Core
> Issue Type: Bug
> Components: modules/spatial
> Affects Versions: 4.0-ALPHA
> Reporter: Neil Hooey
> Assignee: David Smiley
> Labels: distance, geometric
>
> The Lucene vectorDistance() function's Manhattan distance function is
> incorrect.
> Wikipedia says: http://en.wikipedia.org/wiki/Manhattan_distance
> "Taxicab geometry, blahblahblah, is a form of geometry in which the usual
> distance function or metric of Euclidean geometry is replaced by a new metric
> in which the distance between two points is the sum of the *absolute
> differences* of their coordinates."
> The Lucene function isn't taking the absolute value before subtracting the
> vector coordinates.
> I don't have a patch, but the offending code is here:
> {code}
> //
> lucene/contrib/spatial/src/java/org/apache/lucene/spatial/DistanceUtils.java
> } else if (power == 1.0) {
> for (int i = 0; i < vec1.length; i++) {
> result += vec1[i] - vec2[i];
> }
> {code}
> It just needs to use Math.abs() when subtracting the coordinates.
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