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​(uk.ac.starlink.table.StarTable pixTable,
                    long nside,
                    boolean nested)
             throws java.io.IOException

  Constructor.

  Parameters:

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

  nside - HEALPix nside value

  nested - true for nested pixel order, false for ring

  Throws:

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

Method Detail

• sampleValue

  public java.lang.Object sampleValue​(int icol,
                                      double alphaDeg,
                                      double deltaDeg,
                                      double radiusDeg,
                                      PixSampler.StatMode statMode)
                               throws java.io.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:

  java.io.IOException

• sampleValues

  public java.lang.Object[] sampleValues​(double alphaDeg,
                                         double deltaDeg,
                                         double radiusDeg,
                                         PixSampler.StatMode statMode)
                                  throws java.io.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:

  java.io.IOException

• getValueInfos

  public uk.ac.starlink.table.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​(uk.ac.starlink.table.StarTable pixTable)
                                     throws java.io.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 nside is inferred. Parameters are interrogated in accordance with the conventions used by, for instance the FITS files used at NASA's LAMBDA archive, but other HEALPix tables that work in a more or less similar way will probably work.

  I don't know of any proper reference for encoding of HEALPix maps in FITS files, but the documentation for the HPIC package (http://cmb.phys.cwru.edu/hpic/) has a useful list of heuristics (manual section 2.10.1). One of these acknowledges the fact that some HEALPix FITS files have columns which are 1024-element arrays (TFORMn = '1024E'). This routine does not currently support this rather perverse convention. If somebody requests it, maybe I'll consider implementing it.

  Parameters:

  pixTable - random access table containing HEALPix pixels

  Returns:

  PixSampler object taking data from table

  Throws:

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

• inferNested

  public static java.lang.Boolean inferNested​(uk.ac.starlink.table.StarTable pixTable)

  Tries to work out whether a given table uses the nested or ring HEALPix ordering scheme. Parameters are interrogated in accordance with the conventions used by, for instance the FITS files used at NASA's LAMBDA archive.

  Parameters:

  pixTable - pixel data table

  Returns:

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

• inferNside

  public static int inferNside​(uk.ac.starlink.table.StarTable pixTable)
                        throws java.io.IOException

  Tries to work out the HEALPix nside 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 nside result in an error.

  Parameters:

  pixTable - pixel data table

  Returns:

  HEALPix nside

  Throws:

  java.io.IOException