[fitsbits] [EXTERNAL] Re: Stokes parameters coordinate system

[THIERRY FORVEILLE]

> I am not aware of any standard convention for defining the polarization
> convention in use in a FITS file.
> 
> The position angle of the electric vector and hence Q and U may be referred to
> Galactic north, Equatorial north, or an instrument frame, and in practice the
> frame of the polarization (equatorial or Galactic for example) is not always
> the same as that used for the angular coordinates of the image.
> 
I have always assumed that the frame of the polarization in a FITS file is the same 
as that of the coordinates. That might very well not be written anywhere in the 
standard, but it (still) seems a reasonable default to me.