Class 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
    • 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 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'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 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 calling DescribedValue.setValue(java.lang.Object) on the returned objects.
        Returns:
        array of described values which influence the match
      • getMatchScoreInfo

        public uk.ac.starlink.table.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