Tim,
> > Note the IMAGFREQ support for DSB instruments.
>
> When we switch to NDF writing in ACSIS we will have to have two specframes
> in dual sideband instruments. I don't think IMAGFREQ support will be
> possible in the AST encoding unless SpecFrames themselves are extended to
> support dual sideband frames (there would need to be two or three new
> attributes, one to indicate which sideband is current (and which was the
> primary sideband), the other to indicate the IF. Switching to the image
> sideband essentially means adding or subtracting the IF and multiplying
> CDELT by -1. Maybe there could be a DSBSpecFrame which inherits from
> SpecFrame).
The best way to do this depends on what you want to do with the WCS. As an
example, you have two DSB data sets, A and B. In A, the current WCS
Frame represents the lower sideband, and in B it represents the upper
sideband. You then do a WCSALIGN to align A and B. Should WCSALIGN take
account of the differnce in sideband or not? That is, should WCSALIGN
remap B so that the axis represents the lower sideband?
David
|