uk.ac.starlink.table.join
Class HtmSkyPixellator

java.lang.Object
  extended by uk.ac.starlink.table.join.HtmSkyPixellator
All Implemented Interfaces:
SkyPixellator

public class HtmSkyPixellator
extends java.lang.Object
implements SkyPixellator

Implements sky pixellisation using the HTM (Hierarchical Triangular Mesh) indexing scheme.

Note that the HealpixSkyPixellator implementation normally gives much faster matching than this and should generally be used in preference.

See Also:
http://www.skyserver.org/htm/doc/java/index.html

Constructor Summary
HtmSkyPixellator()
          Constructor.
 
Method Summary
 int calculateDefaultLevel(double scale)
          Determines a default value to use for the level paramer based on a given scale.
 int getLevel()
          Returns the HTM level, which determines sky pixel size.
 java.lang.Object[] getPixels(double alpha, double delta, double radius)
          Returns an array of objects representing pixels in a given region.
 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 setLevel(int level)
          Sets the HTM level value, which determines sky pixel size.
 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
 

Constructor Detail

HtmSkyPixellator

public HtmSkyPixellator()
Constructor.

Method Detail

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

getPixels

public java.lang.Object[] getPixels(double alpha,
                                    double delta,
                                    double radius)
Description copied from interface: SkyPixellator
Returns an array of objects representing pixels in a given region. The parameters specify a small circle on the sphere; any pixels which overlap this circle must be returned (additional pixels may also be returned). The output objects are of some opaque type, but must implement the equals and hashCode methods appropriately, so that objects returned from one call can be compared for identity with objects returned from a subsequent call. This comparability is only guaranteed to work if the pixel scale is not changed in between calls.

Specified by:
getPixels in interface SkyPixellator
Parameters:
alpha - right ascension of circle centre in radians
delta - declination of circle centre in radians
radius - radius of circle in radians
Returns:
array of opaque but comparable pixel objects

setLevel

public void setLevel(int level)
Sets the HTM level value, which determines sky pixel size. May be in the range 0 (90deg) to 24 (0.01"). If set to -1, a suitable value will be used based on the scale.

Parameters:
level - new level value

getLevel

public int getLevel()
Returns the HTM level, which determines sky pixel size. The returned value may be the result of a default determination based on scale if no explicit level has been set hitherto, and a non-zero scale is available.

Returns:
level level value used by this engine

calculateDefaultLevel

public int calculateDefaultLevel(double scale)
Determines a default value to use for the level paramer based on a given scale.

Parameters:
scale - sky distance scale angle, in radians