def METHOD_NAME(self):
    """
    Returns the (shower) axis. 
    The axis is antiparallel to the movement of the shower particla and point
    towards the origin of the shower.
    Returns
    -------
    np.array(3,)  
        Shower axis
    """
    if not self.has_parameter(parameters.showerParameters.azimuth) or \
       not self.has_parameter(parameters.showerParameters.zenith):
        logger.error(
            "Azimuth or zenith angle not set! Can not return shower axis.")
        raise ValueError(
            "Azimuth or zenith angle not set! Can not return shower axis.")
    return hp.spherical_to_cartesian(self.get_parameter(parameters.showerParameters.zenith),
                                     self.get_parameter(parameters.showerParameters.azimuth))