Package uk.ac.starlink.table.join

Class HealpixSkyPixellator

java.lang.Object
uk.ac.starlink.table.join.HealpixSkyPixellator
All Implemented Interfaces:
SkyPixellator
Direct Known Subclasses:
CdsHealpixSkyPixellator
public abstract class HealpixSkyPixellator extends Object implements SkyPixellator
Implements sky pixellisation using the HEALPix scheme. This works better than the HTM-based one for two reasons:
  1. It tends to be much faster to calculate a list of small pixels in a region, since the calculations are not hierarchical
  2. The pixels are square which means they generally have fewer neighbours than triangular HTM ones of a similar size
Author:
Mark Taylor (Starlink)

  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    protected
    HealpixSkyPixellator(int maxK)
    Constructor.

  • Method Summary

    Modifier and Type
    Method
    Description
    abstract int
    calculateDefaultK(double scale)
    Determines a default value to use for the HEALPix k parameter based on a given scale.
    protected abstract void
    configureK(int k)
    Updates internal state for the current value of the k parameter.
    int
    getHealpixK()
    Returns the HEALPix k value, which determines sky pixel size, equivalent to log2(nside).
    int
    getMaxK()
    Returns the maximum permissible K value.
    double
    getScale()
    Returns the most recently set angular scale.
    uk.ac.starlink.table.DescribedValue
    getTuningParameter()
    Returns a parameter whose value may be adjusted to alter the pixellisation scale.
    void
    setHealpixK(int healpixK)
    Sets the HEALPix k value, which determines sky pixel size, equivalent to log2(nside).
    void
    setScale(double scale)
    Sets the characteristic angular scale for this pixellator.

    Methods inherited from class java.lang.Object

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

    Methods inherited from interface uk.ac.starlink.table.join.SkyPixellator

    createFixedRadiusPixerFactory, createVariableRadiusPixerFactory

  • Constructor Details

    • HealpixSkyPixellator

      protected HealpixSkyPixellator(int maxK)
      Constructor.
      Parameters:
      maxK - the maximum K value permitted by this implementation

  • Method Details

    • getMaxK

      public int getMaxK()
      Returns the maximum permissible K value.
      Returns:
      maximum Healpix K parameter supported by this implementation

    • setScale

      public void setScale(double scale)
      Description copied from interface: SkyPixellator
      Sets the characteristic angular scale for this pixellator. Pixels should be approximately the size given, so that a larger scale corresponds to larger pixel sizes. The details of pixel size are determined by the details of the pixellation scheme however.
      Specified by:
      setScale in interface SkyPixellator
      Parameters:
      scale - pixel length scale in radians

    • getScale

      public double getScale()
      Description copied from interface: SkyPixellator
      Returns the most recently set angular scale.
      Specified by:
      getScale in interface SkyPixellator
      Returns:
      pixel length scale in radians

    • getTuningParameter

      public uk.ac.starlink.table.DescribedValue getTuningParameter()
      Description copied from interface: SkyPixellator
      Returns a parameter whose value may be adjusted to alter the pixellisation scale. This is not necessarily the same as the scale attribute (its value need not be an angle).
      Specified by:
      getTuningParameter in interface SkyPixellator
      Returns:
      tuning parameter

    • setHealpixK

      public void setHealpixK(int healpixK)
      Sets the HEALPix k value, which determines sky pixel size, equivalent to log2(nside). May be in the range 0 (60deg) to getMaxK(). If set to -1, a suitable value will be used based on the scale.
      Parameters:
      healpixK - new k value

    • getHealpixK

      public int getHealpixK()
      Returns the HEALPix k value, which determines sky pixel size, equivalent to log2(nside). The returned may be the result of a default determination based on scale if no explicit K value has been set hitherto, and a non-zero scale is available.
      Returns:
      k value used by this engine

    • configureK

      protected abstract void configureK(int k)
      Updates internal state for the current value of the k parameter.
      Parameters:
      k - HEALPix order

    • calculateDefaultK

      public abstract int calculateDefaultK(double scale)
      Determines a default value to use for the HEALPix k parameter based on a given scale.
      Parameters:
      scale - distance scale, in radians