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Requirements for a Successful Write Operation

When writing a FrameSet in which the WCS Frame is a SkyFrame to a FitsChan, success depends on the following conditions being met:

  1. The Mapping from pixel coordinates (the base Frame in the FrameSet) to the WCS SkyFrame includes a WcsMap.
  2. The Mapping prior to the WcsMap (i.e. from pixel to IWC) is linear.
  3. The Mapping after the WcsMap (i.e. from native spherical to celestial coordinates) is a spherical rotation for the celestial axes, and linear for any other axes.
  4. The TabOK attribute is set to a non-zero positive value in the FitsChan, and the longitude and latitude axes are separable. In this case the Mapping will be described by a pair of 1-dimensional look-up tables, using the ``-TAB'' algorithm described in FITS-WCS paper III.

If none of the above conditions hold, the write operation will be unsuccessful.



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AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council