uk.ac.starlink.table.join
Class IsotropicCartesianMatchEngine

java.lang.Object
  extended by uk.ac.starlink.table.join.AbstractCartesianMatchEngine
      extended by uk.ac.starlink.table.join.IsotropicCartesianMatchEngine
All Implemented Interfaces:
MatchEngine

public class IsotropicCartesianMatchEngine
extends AbstractCartesianMatchEngine

Matcher which matches in an isotropic N-dimensional Cartesian space. Two points are considered matching if they fall within a given error distance of each other. The isotropic scale is used as the error.

Since:
25 Aug 2004

Field Summary
 
Fields inherited from interface uk.ac.starlink.table.join.MatchEngine
NO_BINS
 
Constructor Summary
IsotropicCartesianMatchEngine(int ndim, double err, boolean normaliseScores)
          Constructs a matcher which matches points in an ndim-dimensional Cartesian space.
 
Method Summary
 boolean canBoundMatch()
          Indicates that the MatchEngine.getMatchBounds(java.lang.Comparable[], java.lang.Comparable[]) method can be invoked to provide some sort of useful result.
 java.lang.Object[] getBins(java.lang.Object[] tuple)
          Returns a set of keys for bins into which possible matches for a given tuple might fall.
 double getError()
          Returns the matching error.
 java.lang.Comparable[][] getMatchBounds(java.lang.Comparable[] minTuple, java.lang.Comparable[] maxTuple)
          Given a range of tuple values, returns a range outside which no match to anything within that range can result.
 DescribedValue[] getMatchParameters()
          Returns a set of DescribedValue objects whose values can be modified to modify the matching criteria.
 ValueInfo getMatchScoreInfo()
          Returns a description of the value returned by the MatchEngine.matchScore(java.lang.Object[], java.lang.Object[]) method.
 ValueInfo[] getTupleInfos()
          Returns a set of ValueInfo objects indicating what is required for the elements of each tuple.
 double matchScore(java.lang.Object[] tuple1, java.lang.Object[] tuple2)
          Indicates whether two tuples count as matching each other, and if so how closely.
 void setError(double err)
          Sets the matching error.
 java.lang.String toString()
           
 
Methods inherited from class uk.ac.starlink.table.join.AbstractCartesianMatchEngine
getBinFactor, getIsotropicScale, getNdim, getRadiusBins, getScale, getScaleBins, getTuningParameters, setBinFactor, setIsotropicScale, setScale
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

IsotropicCartesianMatchEngine

public IsotropicCartesianMatchEngine(int ndim,
                                     double err,
                                     boolean normaliseScores)
Constructs a matcher which matches points in an ndim-dimensional Cartesian space. An initial isotropic error margin is specified.

Parameters:
ndim - dimensionality of the space
err - initial maximum distance between two matching points
normaliseScores - true iff you want match scores to be normalised
Method Detail

setError

public void setError(double err)
Sets the matching error.

Parameters:
err - maximum match error

getError

public double getError()
Returns the matching error.

Returns:
maximum match error

getTupleInfos

public ValueInfo[] getTupleInfos()
Description copied from interface: MatchEngine
Returns a set of ValueInfo objects indicating what is required for the elements of each tuple. The length of this array is the number of elements in the tuple. Each element should at least have a defined name and content class. The info's nullable attribute has a special meaning: if true it means that it makes sense for this element of the tuple to be always blank (for instance assigned to no column).

Returns:
array of objects describing the requirements on each element of the tuples used for matching

getMatchParameters

public DescribedValue[] getMatchParameters()
Description copied from interface: MatchEngine
Returns a set of DescribedValue objects whose values can be modified to modify the matching criteria. Typically at least one of these will be some sort of tolerance separation which determines how close tuples must be to count as a match. This match engine's behaviour can be modified by calling DescribedValue.setValue(java.lang.Object) on the returned objects.

Returns:
array of described values which influence the match

getMatchScoreInfo

public ValueInfo getMatchScoreInfo()
Description copied from interface: MatchEngine
Returns a description of the value returned by the MatchEngine.matchScore(java.lang.Object[], java.lang.Object[]) method. The content class should be numeric (though need not be Double), and the name, description and units should be descriptive of whatever the physical significance of the value is. If the result of matchScore is not interesting (for instance, if it's always either 0 or -1), null may be returned.

Returns:
metadata for the match score results

matchScore

public double matchScore(java.lang.Object[] tuple1,
                         java.lang.Object[] tuple2)
Description copied from interface: MatchEngine
Indicates whether two tuples count as matching each other, and if so how closely. If tuple1 and tuple2 are considered as a matching pair, then a non-negative value should be returned indicating how close the match is - the higher the number the worse the match, and a return value of zero indicates a 'perfect' match. If the two tuples do not consitute a matching pair, then a negative number (conventionally -1.0) should be returned. This return value can be thought of as (and will often correspond physically with) the distance in some real or notional space between the points represented by the two submitted tuples.

If there's no reason to do otherwise, the range 0..1 is recommended for successul matches. However, if the result has some sort of physical meaning (such as a distance in real space) that may be used instead.

Parameters:
tuple1 - one tuple
tuple2 - the other tuple
Returns:
'distance' between tuple1 and tuple2; 0 is a perfect match, larger values indicate worse matches, negative values indicate no match

getBins

public java.lang.Object[] getBins(java.lang.Object[] tuple)
Description copied from interface: MatchEngine
Returns a set of keys for bins into which possible matches for a given tuple might fall. The returned objects can be anything, but should have their equals and hashCode methods implemented properly for comparison.

Parameters:
tuple - tuple
Returns:
set of bin keys which might be returned by invoking this method on other tuples which count as matches for the submitted tuple

canBoundMatch

public boolean canBoundMatch()
Description copied from interface: MatchEngine
Indicates that the MatchEngine.getMatchBounds(java.lang.Comparable[], java.lang.Comparable[]) method can be invoked to provide some sort of useful result.

Returns:
true iff getMatchBounds may provide useful information

getMatchBounds

public java.lang.Comparable[][] getMatchBounds(java.lang.Comparable[] minTuple,
                                               java.lang.Comparable[] maxTuple)
Description copied from interface: MatchEngine
Given a range of tuple values, returns a range outside which no match to anything within that range can result. If the tuples on which this engine works represent some kind of space, the input values and output values specify a hyper-rectangular region of this space. In the common case in which the match criteria are based on proximity in this space up to a certain error, this method should return a rectangle which is like the input one but broadened in each direction by an amount corresponding to the error.

Both the input and output rectangles are specified by tuples representing its opposite corners; equivalently, they are the minimum and maximum values of each tuple element. In either the input or output min/max tuples, any element may be null to indicate that no information is available on the bounds of that tuple element (coordinate).

This method can be used by match algorithms which know in advance the range of coordinates they will match against and wish to reduce workload by not attempting matches which are bound to fail.

For example, a 1-d Cartesian match engine with an isotropic match error 0.5 would turn input values of ((0,200),(10,210)) into output values ((-0.5,199.5),(10.5,210.5)).

This method will only be called if MatchEngine.canBoundMatch() returns true. Thus engines that cannot provide any useful information along these lines (for instance because none of its tuple elements is Comparable do not need to implement it in a meaningful way.

Parameters:
minTuple - tuple consisting of the minimum values of each tuple element in a possible match (to put it another way - coordinates of one corner of a tuple-space rectangle containing such a match)
maxTuple - tuple consisting of the maximum values of each tuple element in a possible match (to put it another way - coordinates of the other corner of a tuple-space rectangle containing such a match)
Returns:
2-element array of tuples - effectively (minTuple,maxTuple) broadened by errors
See Also:
MatchEngine.canBoundMatch()

toString

public java.lang.String toString()
Specified by:
toString in class AbstractCartesianMatchEngine

Copyright © 2004 CLRC: Central Laboratory of the Research Councils. All rights reserved.