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From "Neil Hooey (Updated) (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENE-3814) Manhattan distance function is incorrect, not absolute distance between coordinates
Date Tue, 21 Feb 2012 17:40:34 GMT

     [ https://issues.apache.org/jira/browse/LUCENE-3814?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Neil Hooey updated LUCENE-3814:
-------------------------------

    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: 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
>              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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