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
  • Constructor Details

    • EllipseSkyMatchEngine

      public EllipseSkyMatchEngine(SkyPixellator pixellator, double scale)
      Constructor.
      Parameters:
      pixellator - handles sky pixellisation
      scale - initial value for length scale, in radians
  • Method Details

    • 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 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 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