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 and Description
protected	HealpixSkyPixellator(int maxK) Constructor.

Method Summary

Modifier and Type	Method and 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.
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 Detail

HealpixSkyPixellator

protected HealpixSkyPixellator(int maxK)

Constructor.

Parameters:

maxK - the maximum K value permitted by this implementation

Method Detail

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 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