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Specifying a Particular Spectral Coordinate System

Selection of a particular coordinate system is performed simply by setting a value for the SpecFrame's (character string) System attribute. This setting is most conveniently done when the SpecFrame is created. For example, a SpecFrame representing Energy would be created by:

specframe = astSpecFrame( "System=Energy" );

Note that specifying ``System$=$Energy'' also changes the associated Unit (from metres to Joules). This is because the default value of the SpecFrame's Unit attribute depends on the System attribute setting.

You may change the System value at any time, although this is not usually needed. The values supported are set out in the attribute's description in [*] and include a variety of velocity systems, together with frequency, wavelength, energy, wave-number, etc.


next up previous 264
Next: Attributes which Qualify Spectral Coordinate Systems
Up: Spectral Coordinate Systems (SpecFrames)
Previous: Creating a SpecFrame

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 211
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council