def dist_fcn_callable(self):
        """ Return the distance function corresponding to the dist_fcn string. """
        if self.dist_fcn == 'center_distance':
            return center_distance
        else:
            raise Exception('Error: Unknown distance function %s!' % self.dist_fcn)
 Return the distance function corresponding to the dist_fcn string. 
projects/mmdet3d_plugin/datasets/nuscenes_vad_dataset.py