uk.ac.starlink.table.join

Class EllipseSkyMatchEngine

java.lang.Object

uk.ac.starlink.table.join.AbstractSkyMatchEngine

uk.ac.starlink.table.join.EllipseSkyMatchEngine

All Implemented Interfaces:

MatchEngine

Direct Known Subclasses:

EllipseSkyMatchEngine.InDegrees

public class EllipseSkyMatchEngine
extends AbstractSkyMatchEngine

MatchEngine implementation for ellipses on the surface of a (celestial) sphere. The tuples it uses are five-element arrays of Number objects, as follows:

1. alpha: right ascension coordinate of ellipse centre in radians
2. delta: declination coordinate of ellipse centre in radians
3. mu: primary radius of ellipse in radians
4. nu: secondary radius of ellipse in radians
5. 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

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	EllipseSkyMatchEngine.InDegrees 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

Constructor and Description
EllipseSkyMatchEngine(SkyPixellator pixellator, 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 a scale value for the match score.
ValueInfo[]	getTupleInfos() 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.
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

EllipseSkyMatchEngine

public EllipseSkyMatchEngine(SkyPixellator pixellator,
                             double scale)

Constructor.

Parameters:

pixellator - handles sky pixellisation

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

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

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()

Description copied from interface: MatchEngine

Returns a scale value for the match score. The intention is that the result of matchScore/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

toString

public String toString()

Specified by:

toString in class AbstractSkyMatchEngine