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Choice of Axis Ordering

When reading a FrameSet from a FitsChan, WCS axis $i$ in the current Frame of the resulting FrameSet corresponds to axis $i$ in the FITS header.

When writing a FrameSet to a FitsChan, the axis ordering for the FITS header is chosen to make the CDi_j or PCi_j matrix predominately diagonal. This means that the axis numbering in the FITS header will not necessarily be the same as that in the AST Frame.



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AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 211
R.F. Warren-Smith & D.S. Berry
7th December 2012
E-mail:starlink@jiscmail.ac.uk

Copyright (C) 2012 Science \& Technology Facilities Council