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astSkyOffsetMap - Returns a Mapping which goes from absolute coordinates to offset coordinates

Description:
This function returns a Mapping in which the forward transformation transforms a position in the coordinate system given by the System attribute of the supplied SkyFrame, into the offset coordinate system specified by the SkyRef, SkyRefP and SkyRefIs attributes of the supplied SkyFrame.

A UnitMap is returned if the SkyFrame does not define an offset coordinate system.

Synopsis:
AstMapping $*$astSkyOffsetMap( AstSkyFrame $*$this )
Parameters:
this
Pointer to the SkyFrame.
Returned Value:
astSkyOffsetMap()
Pointer to the returned Mapping.
Notes:
  • A null Object pointer (AST__NULL) will be returned if this function is invoked with the AST error status set, or if it should fail for any reason.


next up previous 264
Next: astSlaAdd - Add a celestial coordinate conversion to an SlaMap
Up: AST Function Descriptions
Previous: astSkyFrame - Create a SkyFrame

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