def shift_coordinate_grid(self, x_shift, y_shift, pixel_unit=False):
        """
        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
        """
        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)
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