code: def ipix_swap_axes(self, ipix, colwise=False):
          
          xy = self.ipix_to_xypix(ipix, colwise)
          return self.xypix_to_ipix(xy, not colwise)
docs: Return the transposed pixel index from the pixel xy coordinates
  
          if colwise is True (False) this assumes the original index was
          in column wise scheme