Class ErrorSkyMatchEngine
- All Implemented Interfaces:
MatchEngine
- Direct Known Subclasses:
ErrorSkyMatchEngine.InDegrees
Number
objects, representing Right Ascension, Declination, and error radius
respectively, all in radians. Other similar longitude/latitude-like
coordinate system may alternatively be used.
Two tuples are considered to match if the distance along a great circle
of their central positions is no greater than the combination
of their per-object radii.
This combination may be either a simple sum or the sum in quadrature,
according to configuration.
A length scale must be supplied, which should be of comparable size to the average per-object error, and which affects performance but not the result. The effect of this is to provide a default for the pixellisation tuning parameter. If the tuning parameter is set directly, the length scale is ignored.
- Since:
- 6 Sep 2011
- Author:
- Mark Taylor
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
MatchEngine class that behaves like ErrorSkyMatchEngine but uses human-friendly units (degrees and arcseconds) rather than radians for tuple elements and match parameters. -
Constructor Summary
ConstructorsConstructorDescriptionErrorSkyMatchEngine
(SkyPixellator pixellator, ErrorSummation errorSummation, double scale) Constructor. -
Method Summary
Modifier and TypeMethodDescriptionReturns a supplier for coverage objects.Returns a factory for MatchKit instances corresponding to the current settings of this object.uk.ac.starlink.table.DescribedValue[]
Returns a set of DescribedValue objects whose values can be modified to modify the matching criteria.uk.ac.starlink.table.ValueInfo
Returns a description of the value returned by theMatchKit.matchScore(java.lang.Object[], java.lang.Object[])
method.double
getScale()
Returns the length scale.double
Returns unity.uk.ac.starlink.table.ValueInfo[]
Returns a set of ValueInfo objects indicating what is required for the elements of each tuple.void
setScale
(double scale) Sets the length scale.toString()
Methods inherited from class uk.ac.starlink.table.join.AbstractSkyMatchEngine
calculateSeparation, getPixellator, getTuningParameters, isSkyPosition
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Constructor Details
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ErrorSkyMatchEngine
Constructor.The
errorSummation
parameter configures how the match score is assessed from the error values of two tuples. The match threshold is determined by summing the error values, either by simple addition or by addition in quadrature.- Parameters:
pixellator
- handles sky pixellisationerrorSummation
- how to combine errors; if null, simple is usedscale
- initial value for length scale, in radians
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Method Details
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setScale
public void setScale(double scale) Sets the length scale.- Overrides:
setScale
in classAbstractSkyMatchEngine
- Parameters:
scale
- rough value of per-object errors, in radians
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getScale
public double getScale()Returns the length scale.- Overrides:
getScale
in classAbstractSkyMatchEngine
- Returns:
- length scale value in radians
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getTupleInfos
public uk.ac.starlink.table.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'snullable
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
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getMatchParameters
public uk.ac.starlink.table.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 callingDescribedValue.setValue(java.lang.Object)
on the returned objects.- Returns:
- array of described values which influence the match
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getMatchScoreInfo
public uk.ac.starlink.table.ValueInfo getMatchScoreInfo()Description copied from interface:MatchEngine
Returns a description of the value returned by theMatchKit.matchScore(java.lang.Object[], java.lang.Object[])
method. The content class should be numeric (though need not beDouble
), and the name, description and units should be descriptive of whatever the physical significance of the value is. If the result ofmatchScore
is not interesting (for instance, if it's always either 0 or -1),null
may be returned.- Returns:
- metadata for the match score results
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createMatchKitFactory
Description copied from interface:MatchEngine
Returns a factory for MatchKit instances corresponding to the current settings of this object.The returned value is immutable, and is not affected by subsequent changes of the settings of this object.
- Returns:
- match kit supplier
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createCoverageFactory
Description copied from interface:MatchEngine
Returns a supplier for coverage objects. Each such coverage can be used to characterise a region of tuple space. When populated with a set of tuples A, any tuple for which the inclusion function defined by itsCoverage.createTestFactory()
method returns false is guaranteed not to match any tuple in A according to this object's match criteria.The returned value is immutable, and is not affected by subsequent changes of the settings of this object.
If no suitable implementation is available, null may be returned.
- Returns:
- supplier of coverage objects, or null
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getScoreScale
public double getScoreScale()Returns unity.- Returns:
- scale of successful match scores, a positive finite number or NaN
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toString
- Specified by:
toString
in classAbstractSkyMatchEngine
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