This attribute is a boolean value which is used when a FrameSetFrameSet is
read from a FitsChanFitsChan with a foreign FITS encoding (e.g. FITS-WCS) using
astReadastRead.
If it has a non-zero value then the returned FrameSet will include
Frames representing "intermediate world coordinates" (IWC). These
Frames will have DomainDomain name "IWC" for primary axis descriptions, and
"IWCa" for secondary axis descriptions, where "a" is replaced by
the single alternate axis description character, as used in the
FITS-WCS header. The default value for "Iwc" is zero.
FITS-WCS paper 1 defines IWC as a Cartesian coordinate system with one
axis for each WCS axis, and is the coordinate system produced by the
rotation matrix (represented by FITS keyword PCi_j, CDi_j, etc).
For instance, for a 2-D FITS-WCS header describing projected
celestial longitude and latitude, the intermediate world
coordinates represent offsets in degrees from the reference point
within the plane of projection.