[ https://issues.apache.org/jira/browse/LUCENE3814?page=com.atlassian.jira.plugin.system.issuetabpanels:alltabpanel
]
Neil Hooey updated LUCENE3814:

Description:
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.
was:
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.
> Manhattan distance function is incorrect, not absolute distance between coordinates
> 
>
> Key: LUCENE3814
> URL: https://issues.apache.org/jira/browse/LUCENE3814
> Project: Lucene  Java
> Issue Type: Bug
> Components: modules/spatial
> Affects Versions: 4.0
> Reporter: Neil Hooey
> 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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