code: def shift_coordinate_grid(self, x_shift, y_shift, pixel_unit=False):
          
          self._coords.shift_coordinate_grid(x_shift, y_shift, pixel_unit=pixel_unit)
          self._x_grid, self._y_grid = self._coords.coordinate_grid(self.nx)
docs: shifts the coordinate system
          :param x_shif: shift in x (or RA)
          :param y_shift: shift in y (or DEC)
          :param pixel_unit: bool, if True, units of pixels in input, otherwise RA/DEC
          :return: updated data class with change in coordinate system