def METHOD_NAME(
    self,
    x,
    y,
    tangential_stretch,
    radial_stretch,
    curvature,
    direction,
    center_x,
    center_y,
):
    """
    ATTENTION: there may not be a global lensing potential!
    :param x:
    :param y:
    :param tangential_stretch: float, stretch of intrinsic source in tangential direction
    :param radial_stretch: float, stretch of intrinsic source in radial direction
    :param curvature: 1/curvature radius
    :param direction: float, angle in radian
    :param center_x: center of source in image plane
    :param center_y: center of source in image plane
    :return:
    """
    theta_E, gamma, center_x_spp, center_y_spp = self.stretch2spp(
        tangential_stretch, radial_stretch, curvature, direction, center_x, center_y
    )
    f_ = self._spp.METHOD_NAME(x, y, theta_E, gamma, center_x_spp, center_y_spp)
    alpha_x, alpha_y = self._spp.derivatives(
        center_x, center_y, theta_E, gamma, center_x_spp, center_y_spp
    )
    f_0 = alpha_x * (x - center_x) + alpha_y * (y - center_y)
    return f_ - f_0