class TrackState:
"""
Enumeration type for the single target track state. Newly created tracks are
classified as `tentative` until enough evidence has been collected. Then,
the track state is changed to `confirmed`. Tracks that are no longer alive
are classified as `deleted` to mark them for removal from the set of active
tracks.
"""
Tentative = 1
Confirmed = 2
Deleted = 3
class Track:
"""
A single target track with state space `(x, y, a, h)` and associated
velocities, where `(x, y)` is the center of the bounding box, `a` is the
aspect ratio and `h` is the height.
Parameters
----------
mean : ndarray
Mean vector of the initial state distribution.
covariance : ndarray
Covariance matrix of the initial state distribution.
track_id : int
A unique track identifier.
n_init : int
Number of consecutive detections before the track is confirmed. The
track state is set to `Deleted` if a miss occurs within the first
`n_init` frames.
max_age : int
The maximum number of consecutive misses before the track state is
set to `Deleted`.
feature : Optional[ndarray]
Feature vector of the detection this track originates from. If not None,
this feature is added to the `features` cache.
Attributes
----------
mean : ndarray
Mean vector of the initial state distribution.
covariance : ndarray
Covariance matrix of the initial state distribution.
track_id : int
A unique track identifier.
hits : int
Total number of measurement updates.
age : int
Total number of frames since first occurance.
time_since_update : int
Total number of frames since last measurement update.
state : TrackState
The current track state.
features : List[ndarray]
A cache of features. On each measurement update, the associated feature
vector is added to this list.
"""
def __init__(self, mean, covariance, track_id, class_id, n_init, max_age,
feature=None):
self.mean = mean
self.covariance = covariance
self.track_id = track_id
self.class_id = class_id
self.hits = 1
self.age = 1
self.time_since_update = 0
self.state = TrackState.Tentative
self.features = []
if feature is not None:
self.features.append(feature)
self._n_init = n_init
self._max_age = max_age
def to_tlwh(self):
"""Get current position in bounding box format `(top left x, top left y,
width, height)`.
Returns
-------
ndarray
The bounding box.
"""
ret = self.mean[:4].copy()
ret[2] *= ret[3]
ret[:2] -= ret[2:] / 2
return ret
def to_tlbr(self):
"""Get current position in bounding box format `(min x, miny, max x,
max y)`.
Returns
-------
ndarray
The bounding box.
"""
ret = self.to_tlwh()
ret[2:] = ret[:2] + ret[2:]
return ret
def increment_age(self):
self.age += 1
self.time_since_update += 1
def predict(self, kf):
"""Propagate the state distribution to the current time step using a
Kalman filter prediction step.
Parameters
----------
kf : kalman_filter.KalmanFilter
The Kalman filter.
"""
self.mean, self.covariance = kf.predict(self.mean, self.covariance)
self.increment_age()
def update(self, kf, detection):
"""Perform Kalman filter measurement update step and update the feature
cache.
Parameters
----------
kf : kalman_filter.KalmanFilter
The Kalman filter.
detection : Detection
The associated detection.
"""
self.mean, self.covariance = kf.update(
self.mean, self.covariance, detection.to_xyah())
self.features.append(detection.feature)
self.hits += 1
self.time_since_update = 0
if self.state == TrackState.Tentative and self.hits >= self._n_init:
self.state = TrackState.Confirmed
def mark_missed(self):
"""Mark this track as missed (no association at the current time step).
"""
if self.state == TrackState.Tentative:
self.state = TrackState.Deleted
elif self.time_since_update > self._max_age:
self.state = TrackState.Deleted
def is_tentative(self):
"""Returns True if this track is tentative (unconfirmed).
"""
return self.state == TrackState.Tentative
def is_confirmed(self):
"""Returns True if this track is confirmed."""
return self.state == TrackState.Confirmed
def is_deleted(self):
"""Returns True if this track is dead and should be deleted."""
return self.state == TrackState.Deleted
