Class EllipseSkyMatchEngine
- All Implemented Interfaces:
MatchEngine
- Direct Known Subclasses:
EllipseSkyMatchEngine.InDegrees
Number
objects, as follows:
- alpha: right ascension coordinate of ellipse centre in radians
- delta: declination coordinate of ellipse centre in radians
- mu: primary radius of ellipse in radians
- nu: secondary radius of ellipse in radians
- zeta: position angle in radians (from north pole to primary radius, in direction of positive alpha axis)
Two tuples are considered to match if their ellipses touch or partially overlap. The match score is a normalized value; it is zero for concentric ellipses, 1 if the centre of one ellipse falls on the circumference of the other, and 2 if the ellipses just touch. Intermediate values are assumed for intermediate situations.
Other RA/Dec-like sky coordinate systems may alternatively be used for the alpha/delta coordinates.
The calculations are approximate since in some cases they rely on projecting the ellipses onto a Cartesian plane before evaluating the match, so for large ellipses the criterion will be less exact. For objects the size of most observed stars and galaxies, this approximation is not expected to be problematic.
The calculations are currently done using numerical optimisation.
- Since:
- 30 Aug 2011
- Author:
- Mark Taylor
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
MatchEngine class that behaves like EllipseSkyMatchEngine but uses human-friendly units (degrees and arcseconds) rather than radians for tuple elements and match parameters. -
Constructor Summary
Constructors -
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 a scale value for the match score.uk.ac.starlink.table.ValueInfo[]
Returns a set of ValueInfo objects indicating what is required for the elements of each tuple.void
setRecogniseCircles
(boolean recogniseCircles) Determines whether short cuts should be taken in the calculations when the ellipses are actually circles.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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EllipseSkyMatchEngine
Constructor.- Parameters:
pixellator
- handles sky pixellisationscale
- 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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setRecogniseCircles
public void setRecogniseCircles(boolean recogniseCircles) Determines whether short cuts should be taken in the calculations when the ellipses are actually circles. This is generally a good idea, since it is faster and improves accuracy; the default is therefore true. But you might want to turn it off for purposes of debugging or testing.- Parameters:
recogniseCircles
- whether to take circle-specific short cuts
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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()Description copied from interface:MatchEngine
Returns a scale value for the match score. The intention is that the result ofmatchScore
/MatchEngine.getScoreScale()
is of order unity, and is thus comparable between different match engines.As a general rule, the result should be the maximum value ever returned from the
matchScore
method, corresponding to the least good successful match. For binary MatchEngine implementations (all matches are either score=0 or failures) a value of 1 is recommended. If nothing reliable can be said about the scale, NaN may be returned.- 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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