Manhattan distance function is incorrect, not absolute distance between
coordinates
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Key: LUCENE-3814
URL: https://issues.apache.org/jira/browse/LUCENE-3814
Project: Lucene - Java
Issue Type: Bug
Components: modules/spatial
Affects Versions: 4.0
Reporter: Neil Hooey
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."
I don't have a patch, but the offending code is here:
// 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];
}
It just needs to use Math.abs() when subtracting the coordinates.
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