HealpixSkyPixellator (Starjava Table API)

java.lang.Object
- uk.ac.starlink.table.join.HealpixSkyPixellator

All Implemented Interfaces:

SkyPixellator

Direct Known Subclasses:

PixtoolsHealpixSkyPixellator
```
public abstract class HealpixSkyPixellator
extends java.lang.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.

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

Method Summary

All Methods Instance Methods Abstract Methods Concrete Methods
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.
`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
getPixels

- 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

Class HealpixSkyPixellator

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

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

Constructor Detail

HealpixSkyPixellator

Method Detail

getMaxK

setScale

getScale

getTuningParameter

setHealpixK

getHealpixK

configureK

calculateDefaultK