uk.ac.starlink.table.join

Class ErrorSkyMatchEngine

java.lang.Object

uk.ac.starlink.table.join.AbstractSkyMatchEngine

uk.ac.starlink.table.join.ErrorSkyMatchEngine

All Implemented Interfaces:

MatchEngine

Direct Known Subclasses:

ErrorSkyMatchEngine.InDegrees

public class ErrorSkyMatchEngine
extends AbstractSkyMatchEngine

MatchEngine which matches objects on the celestial sphere according to per-object error radii. The tuples it uses are three-element arrays of 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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	ErrorSkyMatchEngine.InDegrees 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

Constructors

Constructor and Description
ErrorSkyMatchEngine(SkyPixellator pixellator, ErrorSummation errorSummation, double scale) Constructor.

Method Summary

Modifier and Type	Method and Description
java.util.function.Supplier<Coverage>	createCoverageFactory() Returns a supplier for coverage objects.
java.util.function.Supplier<MatchKit>	createMatchKitFactory() Returns a factory for MatchKit instances corresponding to the current settings of this object.
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 MatchKit.matchScore(java.lang.Object[], java.lang.Object[]) method.
double	getScale() Returns the length scale.
double	getScoreScale() Returns unity.
ValueInfo[]	getTupleInfos() Returns a set of ValueInfo objects indicating what is required for the elements of each tuple.
void	setScale(double scale) Sets the length scale.
String	toString()

Methods inherited from class uk.ac.starlink.table.join.AbstractSkyMatchEngine

calculateSeparation, getPixellator, getTuningParameters, isSkyPosition

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

ErrorSkyMatchEngine

public ErrorSkyMatchEngine(SkyPixellator pixellator,
                           ErrorSummation errorSummation,
                           double scale)

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 pixellisation

errorSummation - how to combine errors; if null, simple is used

scale - initial value for length scale, in radians

Method Detail

setScale

public void setScale(double scale)

Sets the length scale.

Overrides:

setScale in class AbstractSkyMatchEngine

Parameters:

scale - rough value of per-object errors, in radians

getScale

public double getScale()

Returns the length scale.

Overrides:

getScale in class AbstractSkyMatchEngine

Returns:

length scale value in radians

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 MatchKit.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

createMatchKitFactory

public java.util.function.Supplier<MatchKit> 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

createCoverageFactory

public java.util.function.Supplier<Coverage> 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 its Coverage.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

getScoreScale

public double getScoreScale()

Returns unity.

Returns:

scale of successful match scores, a positive finite number or NaN

toString

public String toString()

Specified by:

toString in class AbstractSkyMatchEngine