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 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

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