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Example FITS WCS files


Example FITS maps have been prepared for each of the projections described in Paper II, and separate FITS spectral data files are provided to illustrate the spectral representations described in Paper III.

The example maps (2.5MiB) were constructed with continuum data from the Parkes HIPASS survey (HI radio line) using gridding software based on WCSLIB. The maps use the same projection parameters as in Paper II (where applicable). The particular field chosen contains the southern radio calibration source 1934-638.

Similar image parameters were used for each map; each is 192 x 192 pixels in size with pixel spacing (CDELTi) of 4 arcmin in each direction at the reference point which is at the south celestial pole. The reference pixel (CRPIXj ) was adjusted independently so that each image is centred with pixel coordinate (97,97) at equatorial (J2000) coordinates (18:59:51,-66:15:57), coincident with a 1.5Jy point source.

Because the maps are offset some 25° from the reference point, non-linear distortions are clearly evident. An image based on the NCP projection is also included, although because the reference point is at the south celestial pole it is identical to the SIN projection.

The example spectra (112kiB) are based on an observation of the 13C16O molecular line at 110.2GHz in the Orion Kleinmann-Low nebula using the Mopra radio telescope (data kindly supplied by Andrew Walsh, JCU). While the spectral correlator necessarily produced spectra on a linear frequency axis, the data have been regridded separately into linear wavelength and relativistic velocity. For each of these three basic spectral types, representations are given in terms of frequency, photon energy, wave number, radio velocity, wavelength, optical velocity, redshift, relativistic velocity, and relativistic beta. Thanks to Dirk Petry (ESO) for assistance in this effort.

Each spectral FITS file is actually provided in two forms, one with only a single axis, and the second with four axes of which all but the first (spectral) axis is degenerate. This is for the benefit of FITS interpreting software that distinguishes (erroneously) between one-dimensional images and images that appear to be multi-dimensional but in reality are not. The two forms differ only in their NAXIS and NAXISj keyvalues.

The example maps and spectra are offered mainly as test material for software that deals with FITS WCS. The maps may also be obtained individually via the links below, including the HEALPix projection as of 2005-03-07.

Zenithal (azimuthal) projections
  AZP Zenithal perspective
  SZP Slant zenithal perspective
  TAN Gnomonic
  STG Stereographic
  SIN Generalized orthographic
  NCP North Celestial Pole (SIN special case)
  ARC Zenithal equidistant
  ZPN Zenithal polynomial
  ZEA Zenithal equal area
  AIR Airy's
Cylindrical projections
  CYP Cylindrical perspective
  CEA Cylindrical equal area
  CAR Plate carrée
  MER Mercator's
Pseudo-cylindrical projections
  SFL Sanson-Flamsteed
  PAR Parabolic
  MOL Mollweide's
Conventional projections
  AIT Aitov's
Conic projections
  COP Conic perspective
  COE Conic equal area
  COD Conic equidistant
  COO Conic orthomorphic
Polyconic projections
  BON Bonne's
  PCO Polyconic
Quad-cube projections
  TSC Tangential spherical cube
  CSC COBE quad-cube
  QSC Quadrilateral spherical cube
HEALPix projection

Dr. Mark R. Calabretta ( mcalabre@atnf.csiro.au)
Last modified: 2009/12/11