next up previous 264
Next: Paper I - General Linear Coordinates
Up: AST A Library for Handling World Coordinate Systems in Astronomy
Previous: astStringCase - Convert a string to upper or lower case


FITS-WCS Coverage

This appendix gives details of the FitsChan class implementation of the conventions described in the FITS-WCS papers available at http://fits.gsfc.nasa.gov/fits_wcs.html. These conventions are used only if the Encoding attribute of the FitsChan has the value ``FITS-WCS'' (whether set explicitly or defaulted). It should always be possible for a FrameSet to be read (using the astRead function) from a FitsChan containing a header which conforms to these conventions. However, only those FrameSets which are compatible with the FITS-WCS model can be written to a FitsChan using the astWrite function. For instance, if the current Frame of a FrameSet is re-mapped using, say, an arbitrary MathMap then the FrameSet will no longer be compatible with the FITS-WCS model, and so will not be written out successfully to a FitsChan.

The following sub-sections describe the details of the implementation of each of the first four FITS-WCS papers. Here, the term ``pixel axes'' is used to refer to the FITS pixel coordinates (i.e. the centre of the first image pixel has a value 1.0 on each pixel axis); the term ``IWC axes'' is used to refer to the axes of the Intermediate World Coordinate system; and the term ``WCS axes'' is used to refer to the axes of the final physical coordinate system described by the CTYPEi keywords.


Subsections

next up previous 264
Next: Paper I - General Linear Coordinates
Up: AST A Library for Handling World Coordinate Systems in Astronomy
Previous: astStringCase - Convert a string to upper or lower case

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