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Creating a CmpFrame

A very common use for a CmpFrame within astronomy is to represent a ``spectral cube''. This is a 3-dimensional Frame in which one of the axes represents position within a spectrum, and the other two axes represent position on the sky (or some other spatial domain such as the focal plane of a telescope). As an example, we create such a CmpFrame in which axes 1 and 2 represent Right Ascension and Declination (FK5 J2000), and axis 3 represents wavelength (these are the default coordinate Systems represented by a SkyFrame and a SpecFrame respectively):

AstSkyFrame *skyframe;
AstSpecFrame *specframe;
AstCmpFrame *cmpframe;
...
skyframe = astSkyFrame( "" );
specframe = astSpecFrame( "" );
cmpframe = astCmpFrame( skyframe, specframe, "" );

If it was desired to make RA and Dec correspond to axes 1 and 3, with axis 2 being the spectral axis, then the axes of the CmpFrame created above would need to be permuted as follows:

int perm[ 3 ];
...

perm[ 0 ] = 0;
perm[ 1 ] = 2;
perm[ 2 ] = 1;
astPermAxes( cmpframe, perm );


next up previous
Next: The Attributes of a CmpFrame
Up: Compound Frames (CmpFrames)
Previous: Compound Frames (CmpFrames)

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 211
R.F. Warren-Smith & D.S. Berry
30th April 2003
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2003 Central Laboratory of the Research Councils