uk.ac.starlink.ttools.task

Class PixSampler

java.lang.Object

uk.ac.starlink.ttools.task.PixSampler

public class PixSampler
extends Object

Interrogates a HEALPix all-sky map to sample pixel data. The map is supplied in the form of a table (one row per pixel, using HEALPix pixel indices), as used for instance by LAMBDA.

Since:

5 Dec 2011

Author:

Mark Taylor

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	PixSampler.StatMode Defines how statistics are to be acquired from a pixel or set of pixels.

Field Summary

Fields

Modifier and Type	Field and Description
static PixSampler.StatMode	MEAN_MODE StatMode for taking an average.
static PixSampler.StatMode	POINT_MODE StatMode for making point samples.

Constructor Summary

Constructors

Constructor and Description
PixSampler(StarTable pixTable, boolean nested, int order) Constructor.

Method Summary

Modifier and Type	Method and Description
static PixSampler	createPixSampler(StarTable pixTable) Constructs a PixSampler from a given table.
ColumnInfo[]	getValueInfos(PixSampler.StatMode statMode) Returns the metadata for the columns output by the sampler.
static Boolean	inferNested(StarTable pixTable) Tries to work out whether a given table uses the nested or ring HEALPix ordering scheme.
static int	inferOrder(StarTable pixTable) Tries to work out the HEALPix order parameter for a pixel data table.
Object	sampleValue(int icol, double alphaDeg, double deltaDeg, double radiusDeg, PixSampler.StatMode statMode) Samples a single value from a given sky position.
Object[]	sampleValues(double alphaDeg, double deltaDeg, double radiusDeg, PixSampler.StatMode statMode) Samples values from all columns in given table at a given sky position.

Methods inherited from class java.lang.Object

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

Field Detail

POINT_MODE

public static final PixSampler.StatMode POINT_MODE

StatMode for making point samples.

MEAN_MODE

public static final PixSampler.StatMode MEAN_MODE

StatMode for taking an average.

Constructor Detail

PixSampler

public PixSampler(StarTable pixTable,
                  boolean nested,
                  int order)
           throws IOException

Constructor.

Parameters:

pixTable - random access HEALPix-format table (one row per pixel)

nested - true for nested pixel order, false for ring

order - HEALPix order

Throws:

IOException - if the table has the wrong number of rows or is not random access

Method Detail

sampleValue

public Object sampleValue(int icol,
                          double alphaDeg,
                          double deltaDeg,
                          double radiusDeg,
                          PixSampler.StatMode statMode)
                   throws IOException

Samples a single value from a given sky position.

Parameters:

icol - column index of value to sample

alphaDeg - longitude position in degrees

deltaDeg - latitude position in degrees

radiusDeg - radius of disc over which statistics will be gathered (ignored for point-like statMode)

statMode - mode for sampling statistics

Returns:

sampled value at given point

Throws:

IOException

sampleValues

public Object[] sampleValues(double alphaDeg,
                             double deltaDeg,
                             double radiusDeg,
                             PixSampler.StatMode statMode)
                      throws IOException

Samples values from all columns in given table at a given sky position.

Parameters:

alphaDeg - longitude position in degrees

deltaDeg - latitude position in degrees

radiusDeg - radius of disc over which statistics will be gathered (ignored for point-like statMode)

statMode - mode for sampling statistics

Returns:

array of sampled column values at given point

Throws:

IOException

getValueInfos

public ColumnInfo[] getValueInfos(PixSampler.StatMode statMode)

Returns the metadata for the columns output by the sampler.

Parameters:

statMode - mode for sampling statistics

Returns:

array of output metadata objects, one for each output column

createPixSampler

public static PixSampler createPixSampler(StarTable pixTable)
                                   throws IOException

Constructs a PixSampler from a given table. The current implementation works with any table having a row count corresponding to a HEALPix pixel count, the order is inferred.

Parameters:

pixTable - random access table containing HEALPix pixels

Returns:

PixSampler object taking data from table

Throws:

IOException - if table is not random access or does not appear to contain HEALPix data

inferNested

public static Boolean inferNested(StarTable pixTable)

Tries to work out whether a given table uses the nested or ring HEALPix ordering scheme.

Parameters:

pixTable - pixel data table

Returns:

TRUE for nested, FALSE for ring, null for don't know

inferOrder

public static int inferOrder(StarTable pixTable)
                      throws IOException

Tries to work out the HEALPix order parameter for a pixel data table. Mainly it looks at the row count, but if the table obeys HEALPix header conventions any discrepancies between declared and apparent order result in an error.

Parameters:

pixTable - pixel data table

Returns:

HEALPix order

Throws:

IOException