[fitsbits] Representation of polarimetry data in WCS

Hello all,

I've been writing polarimetric FITS files for some time now with no
regards for how others do things, but I'm presently revising my old
code and thought I might take the time to properly standardize it.
But first I need to actually be sure I understand what the standard is!

WCS Paper I defines a 'STOKES' axis convention for storing
polarimetric data, which uses a series of integers to denote the
various Stokes parameters and/or other forms of polarimetry data. WCS
Paper III defines the -TAB convention for representing nonlinear
coordinates via table lookup. It seems like it should be fairly
straightforward to combine these two forms to easily handle arbitrary
arangements of polarimetry data.

Paper III says that the CTYPEn keyword for a -TAB axis should follow
the 4-3 format, using the 4-letter axis type. So then the proper
value to use is 'STOK-TAB', correct?

Next question: Table 7 of WCS Paper I presents the mapping between
integer codes and polarimetry measurements such as Stokes Q or right-
circular polarization. But there are a few possible polarimetry
measurements which are left out of this table, in particular
polarized intensity
(P = sqrt(Q^2+U^2+V^2). Is there any convention on an integer code to
denote that with?

Thanks,

- Marshall