docs: def offsets_from_wcs(frames, pixref):
      '''Compute offsets between frames using WCS information.
  
      :parameter frames: sequence of FITS filenames or file descriptors
      :parameter pixref: numpy array used as reference pixel
  
      The sky world coordinates are computed on *pixref* using
      the WCS of the first frame in the sequence. Then, the
      pixel coordinates of the reference sky world-coordinates
      are computed for the rest of the frames.
  
      The results is a numpy array with the difference between the
      computed pixel value and the reference pixel. The first line
      of the array is [0, 0], being the offset from the first image
      to itself.
  
      '''
  
      result = numpy.zeros((len(frames), pixref.shape[1]))
  
      with frames[0].open() as hdulist:
          wcsh = wcs.WCS(hdulist[0].header)
          skyref = wcsh.wcs_pix2world(pixref, 1)
  
      for idx, frame in enumerate(frames[1:]):
          with frame.open() as hdulist:
              wcsh = wcs.WCS(hdulist[0].header)
              pixval = wcsh.wcs_world2pix(skyref, 1)
              result[idx + 1] = -(pixval[0] - pixref[0])
  
      return result