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Choice of Reference Point

When writing a FrameSet to a FitsChan, the pixel coordinates of the reference point for linear axes (i.e. the CRPIXj values) are chosen as follows:

The pixel to WCS Mapping is then used to find the corresponding CRVALjvalues.

Again, the above procedure is over-ridden if the Frame is a SkyFrame or a SpecFrame, in which case the conventions of papers II and III are used as described below.



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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