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In addition to the image format discussed in the previous sections of this paper (i.e. an N-dimensional array in a FITS primary array or FITS IMAGE extension), there are two other FITS image representations that are used commonly by the astronomical community in binary tables extensions (Cotton et al. [1995]) in the forms of:

  1. a multi-dimensional vector in a single element of a FITS binary table,
  2. a tabulated list of pixel coordinates in a FITS ASCII or binary table, and
  3. a combination of the two forms in a FITS binary table.

The purpose of this section is to define a naming convention for the coordinate system keywords to be used with these alternate image formats. Keywords specific to celestial coordinates will be treated in Paper II and an example will be given. Keywords specific to spectral coordinates will be treated in a section of Paper III. This general convention has been used for some time and is therefore considered part of the full world coordinates convention.

The NOST (Hanisch et al. [2001]) standard provides that the interpretation of raw field values found in any column n of a FITS table (either ASCII or binary) may be transformed into true physical values by the presence of the keywords TZEROn and TSCALn for that column. The tabular WCS keywords defined in this section (and in the corresponding tabular keyword sections of subsequent WCS papers) operate on the true physical values, not on the raw field values. Therefore any transformation specified by TZEROn and TSCALn is to be applied before these tabular WCS computations.

2 Contributed by William Pence, Arnold Rots, and Lorella Angelini of the NASA Goddard Space Flight Center, Greenbelt, MD 20771. Back.

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