Return a copy of self, shifted a constant offset.

        Parameters
        ----------
        offset_value : float
            Number of pixels to shift the CCDLine.

def offset(self, offset_value):
        """Return a copy of self, shifted a constant offset.

        Parameters
        ----------
        offset_value : float
            Number of pixels to shift the CCDLine.

        """

        new_instance = deepcopy(self)
        new_instance.poly_funct.coef[0] += offset_value
        return new_instance