def __init__(self, bbox, delta_t=3, orig=False):
        """
        Initialises a tracker using initial bounding box.

        """
        # define constant velocity model
        if not orig:
          from .kalmanfilter import KalmanFilterNew as KalmanFilter
          self.kf = KalmanFilter(dim_x=7, dim_z=4)
        else:
          from filterpy.kalman import KalmanFilter
          self.kf = KalmanFilter(dim_x=7, dim_z=4)
        self.kf.F = np.array([[1, 0, 0, 0, 1, 0, 0], [0, 1, 0, 0, 0, 1, 0], [0, 0, 1, 0, 0, 0, 1], [
                            0, 0, 0, 1, 0, 0, 0],  [0, 0, 0, 0, 1, 0, 0], [0, 0, 0, 0, 0, 1, 0], [0, 0, 0, 0, 0, 0, 1]])
        self.kf.H = np.array([[1, 0, 0, 0, 0, 0, 0], [0, 1, 0, 0, 0, 0, 0],
                            [0, 0, 1, 0, 0, 0, 0], [0, 0, 0, 1, 0, 0, 0]])

        self.kf.R[2:, 2:] *= 10.
        self.kf.P[4:, 4:] *= 1000.  # give high uncertainty to the unobservable initial velocities
        self.kf.P *= 10.
        self.kf.Q[-1, -1] *= 0.01
        self.kf.Q[4:, 4:] *= 0.01

        self.kf.x[:4] = convert_bbox_to_z(bbox)
        self.time_since_update = 0
        self.id = KalmanBoxTracker.count
        KalmanBoxTracker.count += 1
        self.history = []
        self.hits = 0
        self.hit_streak = 0
        self.age = 0
        """
        NOTE: [-1,-1,-1,-1,-1] is a compromising placeholder for non-observation status, the same for the return of 
        function k_previous_obs. It is ugly and I do not like it. But to support generate observation array in a 
        fast and unified way, which you would see below k_observations = np.array([k_previous_obs(...]]), let's bear it for now.
        """
        self.last_observation = np.array([-1, -1, -1, -1, -1])  # placeholder
        self.observations = dict()
        self.history_observations = []
        self.velocity = None
        self.delta_t = delta_t

        Initialises a tracker using initial bounding box.

        
trackers/ocsort_tracker/ocsort.py