def gm_estimator(gm_list):
    """ GM-PHD State Estimator

    Args:
        gm_list (:obj:`list`): List of Gaussian components representing
            posterior probability hypothesis density of multiple targets.

    Returns:
        (:obj:`list`): List of estimated target states.
    """
    targets = []
    for gm in gm_list:
        if gm.weight > 0.5:
            targets.append(gm.mean)
    return targets