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Reference for ultralytics/trackers/utils/kalman_filter.py

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ultralytics.trackers.utils.kalman_filter.KalmanFilterXYAH

For bytetrack. A simple Kalman filter for tracking bounding boxes in image space.

The 8-dimensional state space (x, y, a, h, vx, vy, va, vh) contains the bounding box center position (x, y), aspect ratio a, height h, and their respective velocities.

Object motion follows a constant velocity model. The bounding box location (x, y, a, h) is taken as direct observation of the state space (linear observation model).

Source code in ultralytics/trackers/utils/kalman_filter.py
class KalmanFilterXYAH:
    """
    For bytetrack. A simple Kalman filter for tracking bounding boxes in image space.

    The 8-dimensional state space (x, y, a, h, vx, vy, va, vh) contains the bounding box center position (x, y), aspect
    ratio a, height h, and their respective velocities.

    Object motion follows a constant velocity model. The bounding box location (x, y, a, h) is taken as direct
    observation of the state space (linear observation model).
    """

    def __init__(self):
        """Initialize Kalman filter model matrices with motion and observation uncertainty weights."""
        ndim, dt = 4, 1.0

        # Create Kalman filter model matrices
        self._motion_mat = np.eye(2 * ndim, 2 * ndim)
        for i in range(ndim):
            self._motion_mat[i, ndim + i] = dt
        self._update_mat = np.eye(ndim, 2 * ndim)

        # Motion and observation uncertainty are chosen relative to the current state estimate. These weights control
        # the amount of uncertainty in the model.
        self._std_weight_position = 1.0 / 20
        self._std_weight_velocity = 1.0 / 160

    def initiate(self, measurement: np.ndarray) -> tuple:
        """
        Create track from unassociated measurement.

        Args:
            measurement (ndarray): Bounding box coordinates (x, y, a, h) with center position (x, y), aspect ratio a,
                and height h.

        Returns:
            (tuple[ndarray, ndarray]): Returns the mean vector (8 dimensional) and covariance matrix (8x8 dimensional)
                of the new track. Unobserved velocities are initialized to 0 mean.
        """
        mean_pos = measurement
        mean_vel = np.zeros_like(mean_pos)
        mean = np.r_[mean_pos, mean_vel]

        std = [
            2 * self._std_weight_position * measurement[3],
            2 * self._std_weight_position * measurement[3],
            1e-2,
            2 * self._std_weight_position * measurement[3],
            10 * self._std_weight_velocity * measurement[3],
            10 * self._std_weight_velocity * measurement[3],
            1e-5,
            10 * self._std_weight_velocity * measurement[3],
        ]
        covariance = np.diag(np.square(std))
        return mean, covariance

    def predict(self, mean: np.ndarray, covariance: np.ndarray) -> tuple:
        """
        Run Kalman filter prediction step.

        Args:
            mean (ndarray): The 8 dimensional mean vector of the object state at the previous time step.
            covariance (ndarray): The 8x8 dimensional covariance matrix of the object state at the previous time step.

        Returns:
            (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
                velocities are initialized to 0 mean.
        """
        std_pos = [
            self._std_weight_position * mean[3],
            self._std_weight_position * mean[3],
            1e-2,
            self._std_weight_position * mean[3],
        ]
        std_vel = [
            self._std_weight_velocity * mean[3],
            self._std_weight_velocity * mean[3],
            1e-5,
            self._std_weight_velocity * mean[3],
        ]
        motion_cov = np.diag(np.square(np.r_[std_pos, std_vel]))

        mean = np.dot(mean, self._motion_mat.T)
        covariance = np.linalg.multi_dot((self._motion_mat, covariance, self._motion_mat.T)) + motion_cov

        return mean, covariance

    def project(self, mean: np.ndarray, covariance: np.ndarray) -> tuple:
        """
        Project state distribution to measurement space.

        Args:
            mean (ndarray): The state's mean vector (8 dimensional array).
            covariance (ndarray): The state's covariance matrix (8x8 dimensional).

        Returns:
            (tuple[ndarray, ndarray]): Returns the projected mean and covariance matrix of the given state estimate.
        """
        std = [
            self._std_weight_position * mean[3],
            self._std_weight_position * mean[3],
            1e-1,
            self._std_weight_position * mean[3],
        ]
        innovation_cov = np.diag(np.square(std))

        mean = np.dot(self._update_mat, mean)
        covariance = np.linalg.multi_dot((self._update_mat, covariance, self._update_mat.T))
        return mean, covariance + innovation_cov

    def multi_predict(self, mean: np.ndarray, covariance: np.ndarray) -> tuple:
        """
        Run Kalman filter prediction step (Vectorized version).

        Args:
            mean (ndarray): The Nx8 dimensional mean matrix of the object states at the previous time step.
            covariance (ndarray): The Nx8x8 covariance matrix of the object states at the previous time step.

        Returns:
            (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
                velocities are initialized to 0 mean.
        """
        std_pos = [
            self._std_weight_position * mean[:, 3],
            self._std_weight_position * mean[:, 3],
            1e-2 * np.ones_like(mean[:, 3]),
            self._std_weight_position * mean[:, 3],
        ]
        std_vel = [
            self._std_weight_velocity * mean[:, 3],
            self._std_weight_velocity * mean[:, 3],
            1e-5 * np.ones_like(mean[:, 3]),
            self._std_weight_velocity * mean[:, 3],
        ]
        sqr = np.square(np.r_[std_pos, std_vel]).T

        motion_cov = [np.diag(sqr[i]) for i in range(len(mean))]
        motion_cov = np.asarray(motion_cov)

        mean = np.dot(mean, self._motion_mat.T)
        left = np.dot(self._motion_mat, covariance).transpose((1, 0, 2))
        covariance = np.dot(left, self._motion_mat.T) + motion_cov

        return mean, covariance

    def update(self, mean: np.ndarray, covariance: np.ndarray, measurement: np.ndarray) -> tuple:
        """
        Run Kalman filter correction step.

        Args:
            mean (ndarray): The predicted state's mean vector (8 dimensional).
            covariance (ndarray): The state's covariance matrix (8x8 dimensional).
            measurement (ndarray): The 4 dimensional measurement vector (x, y, a, h), where (x, y) is the center
                position, a the aspect ratio, and h the height of the bounding box.

        Returns:
            (tuple[ndarray, ndarray]): Returns the measurement-corrected state distribution.
        """
        projected_mean, projected_cov = self.project(mean, covariance)

        chol_factor, lower = scipy.linalg.cho_factor(projected_cov, lower=True, check_finite=False)
        kalman_gain = scipy.linalg.cho_solve(
            (chol_factor, lower), np.dot(covariance, self._update_mat.T).T, check_finite=False
        ).T
        innovation = measurement - projected_mean

        new_mean = mean + np.dot(innovation, kalman_gain.T)
        new_covariance = covariance - np.linalg.multi_dot((kalman_gain, projected_cov, kalman_gain.T))
        return new_mean, new_covariance

    def gating_distance(
        self,
        mean: np.ndarray,
        covariance: np.ndarray,
        measurements: np.ndarray,
        only_position: bool = False,
        metric: str = "maha",
    ) -> np.ndarray:
        """
        Compute gating distance between state distribution and measurements. A suitable distance threshold can be
        obtained from `chi2inv95`. If `only_position` is False, the chi-square distribution has 4 degrees of freedom,
        otherwise 2.

        Args:
            mean (ndarray): Mean vector over the state distribution (8 dimensional).
            covariance (ndarray): Covariance of the state distribution (8x8 dimensional).
            measurements (ndarray): An Nx4 matrix of N measurements, each in format (x, y, a, h) where (x, y)
                is the bounding box center position, a the aspect ratio, and h the height.
            only_position (bool, optional): If True, distance computation is done with respect to the bounding box
                center position only. Defaults to False.
            metric (str, optional): The metric to use for calculating the distance. Options are 'gaussian' for the
                squared Euclidean distance and 'maha' for the squared Mahalanobis distance. Defaults to 'maha'.

        Returns:
            (np.ndarray): Returns an array of length N, where the i-th element contains the squared distance between
                (mean, covariance) and `measurements[i]`.
        """
        mean, covariance = self.project(mean, covariance)
        if only_position:
            mean, covariance = mean[:2], covariance[:2, :2]
            measurements = measurements[:, :2]

        d = measurements - mean
        if metric == "gaussian":
            return np.sum(d * d, axis=1)
        elif metric == "maha":
            cholesky_factor = np.linalg.cholesky(covariance)
            z = scipy.linalg.solve_triangular(cholesky_factor, d.T, lower=True, check_finite=False, overwrite_b=True)
            return np.sum(z * z, axis=0)  # square maha
        else:
            raise ValueError("Invalid distance metric")

__init__()

Initialize Kalman filter model matrices with motion and observation uncertainty weights.

Source code in ultralytics/trackers/utils/kalman_filter.py
def __init__(self):
    """Initialize Kalman filter model matrices with motion and observation uncertainty weights."""
    ndim, dt = 4, 1.0

    # Create Kalman filter model matrices
    self._motion_mat = np.eye(2 * ndim, 2 * ndim)
    for i in range(ndim):
        self._motion_mat[i, ndim + i] = dt
    self._update_mat = np.eye(ndim, 2 * ndim)

    # Motion and observation uncertainty are chosen relative to the current state estimate. These weights control
    # the amount of uncertainty in the model.
    self._std_weight_position = 1.0 / 20
    self._std_weight_velocity = 1.0 / 160

gating_distance(mean, covariance, measurements, only_position=False, metric='maha')

Compute gating distance between state distribution and measurements. A suitable distance threshold can be obtained from chi2inv95. If only_position is False, the chi-square distribution has 4 degrees of freedom, otherwise 2.

Parameters:

Name Type Description Default
mean ndarray

Mean vector over the state distribution (8 dimensional).

required
covariance ndarray

Covariance of the state distribution (8x8 dimensional).

required
measurements ndarray

An Nx4 matrix of N measurements, each in format (x, y, a, h) where (x, y) is the bounding box center position, a the aspect ratio, and h the height.

required
only_position bool

If True, distance computation is done with respect to the bounding box center position only. Defaults to False.

False
metric str

The metric to use for calculating the distance. Options are 'gaussian' for the squared Euclidean distance and 'maha' for the squared Mahalanobis distance. Defaults to 'maha'.

'maha'

Returns:

Type Description
ndarray

Returns an array of length N, where the i-th element contains the squared distance between (mean, covariance) and measurements[i].

Source code in ultralytics/trackers/utils/kalman_filter.py
def gating_distance(
    self,
    mean: np.ndarray,
    covariance: np.ndarray,
    measurements: np.ndarray,
    only_position: bool = False,
    metric: str = "maha",
) -> np.ndarray:
    """
    Compute gating distance between state distribution and measurements. A suitable distance threshold can be
    obtained from `chi2inv95`. If `only_position` is False, the chi-square distribution has 4 degrees of freedom,
    otherwise 2.

    Args:
        mean (ndarray): Mean vector over the state distribution (8 dimensional).
        covariance (ndarray): Covariance of the state distribution (8x8 dimensional).
        measurements (ndarray): An Nx4 matrix of N measurements, each in format (x, y, a, h) where (x, y)
            is the bounding box center position, a the aspect ratio, and h the height.
        only_position (bool, optional): If True, distance computation is done with respect to the bounding box
            center position only. Defaults to False.
        metric (str, optional): The metric to use for calculating the distance. Options are 'gaussian' for the
            squared Euclidean distance and 'maha' for the squared Mahalanobis distance. Defaults to 'maha'.

    Returns:
        (np.ndarray): Returns an array of length N, where the i-th element contains the squared distance between
            (mean, covariance) and `measurements[i]`.
    """
    mean, covariance = self.project(mean, covariance)
    if only_position:
        mean, covariance = mean[:2], covariance[:2, :2]
        measurements = measurements[:, :2]

    d = measurements - mean
    if metric == "gaussian":
        return np.sum(d * d, axis=1)
    elif metric == "maha":
        cholesky_factor = np.linalg.cholesky(covariance)
        z = scipy.linalg.solve_triangular(cholesky_factor, d.T, lower=True, check_finite=False, overwrite_b=True)
        return np.sum(z * z, axis=0)  # square maha
    else:
        raise ValueError("Invalid distance metric")

initiate(measurement)

Create track from unassociated measurement.

Parameters:

Name Type Description Default
measurement ndarray

Bounding box coordinates (x, y, a, h) with center position (x, y), aspect ratio a, and height h.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the mean vector (8 dimensional) and covariance matrix (8x8 dimensional) of the new track. Unobserved velocities are initialized to 0 mean.

Source code in ultralytics/trackers/utils/kalman_filter.py
def initiate(self, measurement: np.ndarray) -> tuple:
    """
    Create track from unassociated measurement.

    Args:
        measurement (ndarray): Bounding box coordinates (x, y, a, h) with center position (x, y), aspect ratio a,
            and height h.

    Returns:
        (tuple[ndarray, ndarray]): Returns the mean vector (8 dimensional) and covariance matrix (8x8 dimensional)
            of the new track. Unobserved velocities are initialized to 0 mean.
    """
    mean_pos = measurement
    mean_vel = np.zeros_like(mean_pos)
    mean = np.r_[mean_pos, mean_vel]

    std = [
        2 * self._std_weight_position * measurement[3],
        2 * self._std_weight_position * measurement[3],
        1e-2,
        2 * self._std_weight_position * measurement[3],
        10 * self._std_weight_velocity * measurement[3],
        10 * self._std_weight_velocity * measurement[3],
        1e-5,
        10 * self._std_weight_velocity * measurement[3],
    ]
    covariance = np.diag(np.square(std))
    return mean, covariance

multi_predict(mean, covariance)

Run Kalman filter prediction step (Vectorized version).

Parameters:

Name Type Description Default
mean ndarray

The Nx8 dimensional mean matrix of the object states at the previous time step.

required
covariance ndarray

The Nx8x8 covariance matrix of the object states at the previous time step.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the mean vector and covariance matrix of the predicted state. Unobserved velocities are initialized to 0 mean.

Source code in ultralytics/trackers/utils/kalman_filter.py
def multi_predict(self, mean: np.ndarray, covariance: np.ndarray) -> tuple:
    """
    Run Kalman filter prediction step (Vectorized version).

    Args:
        mean (ndarray): The Nx8 dimensional mean matrix of the object states at the previous time step.
        covariance (ndarray): The Nx8x8 covariance matrix of the object states at the previous time step.

    Returns:
        (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
            velocities are initialized to 0 mean.
    """
    std_pos = [
        self._std_weight_position * mean[:, 3],
        self._std_weight_position * mean[:, 3],
        1e-2 * np.ones_like(mean[:, 3]),
        self._std_weight_position * mean[:, 3],
    ]
    std_vel = [
        self._std_weight_velocity * mean[:, 3],
        self._std_weight_velocity * mean[:, 3],
        1e-5 * np.ones_like(mean[:, 3]),
        self._std_weight_velocity * mean[:, 3],
    ]
    sqr = np.square(np.r_[std_pos, std_vel]).T

    motion_cov = [np.diag(sqr[i]) for i in range(len(mean))]
    motion_cov = np.asarray(motion_cov)

    mean = np.dot(mean, self._motion_mat.T)
    left = np.dot(self._motion_mat, covariance).transpose((1, 0, 2))
    covariance = np.dot(left, self._motion_mat.T) + motion_cov

    return mean, covariance

predict(mean, covariance)

Run Kalman filter prediction step.

Parameters:

Name Type Description Default
mean ndarray

The 8 dimensional mean vector of the object state at the previous time step.

required
covariance ndarray

The 8x8 dimensional covariance matrix of the object state at the previous time step.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the mean vector and covariance matrix of the predicted state. Unobserved velocities are initialized to 0 mean.

Source code in ultralytics/trackers/utils/kalman_filter.py
def predict(self, mean: np.ndarray, covariance: np.ndarray) -> tuple:
    """
    Run Kalman filter prediction step.

    Args:
        mean (ndarray): The 8 dimensional mean vector of the object state at the previous time step.
        covariance (ndarray): The 8x8 dimensional covariance matrix of the object state at the previous time step.

    Returns:
        (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
            velocities are initialized to 0 mean.
    """
    std_pos = [
        self._std_weight_position * mean[3],
        self._std_weight_position * mean[3],
        1e-2,
        self._std_weight_position * mean[3],
    ]
    std_vel = [
        self._std_weight_velocity * mean[3],
        self._std_weight_velocity * mean[3],
        1e-5,
        self._std_weight_velocity * mean[3],
    ]
    motion_cov = np.diag(np.square(np.r_[std_pos, std_vel]))

    mean = np.dot(mean, self._motion_mat.T)
    covariance = np.linalg.multi_dot((self._motion_mat, covariance, self._motion_mat.T)) + motion_cov

    return mean, covariance

project(mean, covariance)

Project state distribution to measurement space.

Parameters:

Name Type Description Default
mean ndarray

The state's mean vector (8 dimensional array).

required
covariance ndarray

The state's covariance matrix (8x8 dimensional).

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the projected mean and covariance matrix of the given state estimate.

Source code in ultralytics/trackers/utils/kalman_filter.py
def project(self, mean: np.ndarray, covariance: np.ndarray) -> tuple:
    """
    Project state distribution to measurement space.

    Args:
        mean (ndarray): The state's mean vector (8 dimensional array).
        covariance (ndarray): The state's covariance matrix (8x8 dimensional).

    Returns:
        (tuple[ndarray, ndarray]): Returns the projected mean and covariance matrix of the given state estimate.
    """
    std = [
        self._std_weight_position * mean[3],
        self._std_weight_position * mean[3],
        1e-1,
        self._std_weight_position * mean[3],
    ]
    innovation_cov = np.diag(np.square(std))

    mean = np.dot(self._update_mat, mean)
    covariance = np.linalg.multi_dot((self._update_mat, covariance, self._update_mat.T))
    return mean, covariance + innovation_cov

update(mean, covariance, measurement)

Run Kalman filter correction step.

Parameters:

Name Type Description Default
mean ndarray

The predicted state's mean vector (8 dimensional).

required
covariance ndarray

The state's covariance matrix (8x8 dimensional).

required
measurement ndarray

The 4 dimensional measurement vector (x, y, a, h), where (x, y) is the center position, a the aspect ratio, and h the height of the bounding box.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the measurement-corrected state distribution.

Source code in ultralytics/trackers/utils/kalman_filter.py
def update(self, mean: np.ndarray, covariance: np.ndarray, measurement: np.ndarray) -> tuple:
    """
    Run Kalman filter correction step.

    Args:
        mean (ndarray): The predicted state's mean vector (8 dimensional).
        covariance (ndarray): The state's covariance matrix (8x8 dimensional).
        measurement (ndarray): The 4 dimensional measurement vector (x, y, a, h), where (x, y) is the center
            position, a the aspect ratio, and h the height of the bounding box.

    Returns:
        (tuple[ndarray, ndarray]): Returns the measurement-corrected state distribution.
    """
    projected_mean, projected_cov = self.project(mean, covariance)

    chol_factor, lower = scipy.linalg.cho_factor(projected_cov, lower=True, check_finite=False)
    kalman_gain = scipy.linalg.cho_solve(
        (chol_factor, lower), np.dot(covariance, self._update_mat.T).T, check_finite=False
    ).T
    innovation = measurement - projected_mean

    new_mean = mean + np.dot(innovation, kalman_gain.T)
    new_covariance = covariance - np.linalg.multi_dot((kalman_gain, projected_cov, kalman_gain.T))
    return new_mean, new_covariance



ultralytics.trackers.utils.kalman_filter.KalmanFilterXYWH

Bases: KalmanFilterXYAH

For BoT-SORT. A simple Kalman filter for tracking bounding boxes in image space.

The 8-dimensional state space (x, y, w, h, vx, vy, vw, vh) contains the bounding box center position (x, y), width w, height h, and their respective velocities.

Object motion follows a constant velocity model. The bounding box location (x, y, w, h) is taken as direct observation of the state space (linear observation model).

Source code in ultralytics/trackers/utils/kalman_filter.py
class KalmanFilterXYWH(KalmanFilterXYAH):
    """
    For BoT-SORT. A simple Kalman filter for tracking bounding boxes in image space.

    The 8-dimensional state space (x, y, w, h, vx, vy, vw, vh) contains the bounding box center position (x, y), width
    w, height h, and their respective velocities.

    Object motion follows a constant velocity model. The bounding box location (x, y, w, h) is taken as direct
    observation of the state space (linear observation model).
    """

    def initiate(self, measurement: np.ndarray) -> tuple:
        """
        Create track from unassociated measurement.

        Args:
            measurement (ndarray): Bounding box coordinates (x, y, w, h) with center position (x, y), width, and height.

        Returns:
            (tuple[ndarray, ndarray]): Returns the mean vector (8 dimensional) and covariance matrix (8x8 dimensional)
                of the new track. Unobserved velocities are initialized to 0 mean.
        """
        mean_pos = measurement
        mean_vel = np.zeros_like(mean_pos)
        mean = np.r_[mean_pos, mean_vel]

        std = [
            2 * self._std_weight_position * measurement[2],
            2 * self._std_weight_position * measurement[3],
            2 * self._std_weight_position * measurement[2],
            2 * self._std_weight_position * measurement[3],
            10 * self._std_weight_velocity * measurement[2],
            10 * self._std_weight_velocity * measurement[3],
            10 * self._std_weight_velocity * measurement[2],
            10 * self._std_weight_velocity * measurement[3],
        ]
        covariance = np.diag(np.square(std))
        return mean, covariance

    def predict(self, mean, covariance) -> tuple:
        """
        Run Kalman filter prediction step.

        Args:
            mean (ndarray): The 8 dimensional mean vector of the object state at the previous time step.
            covariance (ndarray): The 8x8 dimensional covariance matrix of the object state at the previous time step.

        Returns:
            (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
                velocities are initialized to 0 mean.
        """
        std_pos = [
            self._std_weight_position * mean[2],
            self._std_weight_position * mean[3],
            self._std_weight_position * mean[2],
            self._std_weight_position * mean[3],
        ]
        std_vel = [
            self._std_weight_velocity * mean[2],
            self._std_weight_velocity * mean[3],
            self._std_weight_velocity * mean[2],
            self._std_weight_velocity * mean[3],
        ]
        motion_cov = np.diag(np.square(np.r_[std_pos, std_vel]))

        mean = np.dot(mean, self._motion_mat.T)
        covariance = np.linalg.multi_dot((self._motion_mat, covariance, self._motion_mat.T)) + motion_cov

        return mean, covariance

    def project(self, mean, covariance) -> tuple:
        """
        Project state distribution to measurement space.

        Args:
            mean (ndarray): The state's mean vector (8 dimensional array).
            covariance (ndarray): The state's covariance matrix (8x8 dimensional).

        Returns:
            (tuple[ndarray, ndarray]): Returns the projected mean and covariance matrix of the given state estimate.
        """
        std = [
            self._std_weight_position * mean[2],
            self._std_weight_position * mean[3],
            self._std_weight_position * mean[2],
            self._std_weight_position * mean[3],
        ]
        innovation_cov = np.diag(np.square(std))

        mean = np.dot(self._update_mat, mean)
        covariance = np.linalg.multi_dot((self._update_mat, covariance, self._update_mat.T))
        return mean, covariance + innovation_cov

    def multi_predict(self, mean, covariance) -> tuple:
        """
        Run Kalman filter prediction step (Vectorized version).

        Args:
            mean (ndarray): The Nx8 dimensional mean matrix of the object states at the previous time step.
            covariance (ndarray): The Nx8x8 covariance matrix of the object states at the previous time step.

        Returns:
            (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
                velocities are initialized to 0 mean.
        """
        std_pos = [
            self._std_weight_position * mean[:, 2],
            self._std_weight_position * mean[:, 3],
            self._std_weight_position * mean[:, 2],
            self._std_weight_position * mean[:, 3],
        ]
        std_vel = [
            self._std_weight_velocity * mean[:, 2],
            self._std_weight_velocity * mean[:, 3],
            self._std_weight_velocity * mean[:, 2],
            self._std_weight_velocity * mean[:, 3],
        ]
        sqr = np.square(np.r_[std_pos, std_vel]).T

        motion_cov = [np.diag(sqr[i]) for i in range(len(mean))]
        motion_cov = np.asarray(motion_cov)

        mean = np.dot(mean, self._motion_mat.T)
        left = np.dot(self._motion_mat, covariance).transpose((1, 0, 2))
        covariance = np.dot(left, self._motion_mat.T) + motion_cov

        return mean, covariance

    def update(self, mean, covariance, measurement) -> tuple:
        """
        Run Kalman filter correction step.

        Args:
            mean (ndarray): The predicted state's mean vector (8 dimensional).
            covariance (ndarray): The state's covariance matrix (8x8 dimensional).
            measurement (ndarray): The 4 dimensional measurement vector (x, y, w, h), where (x, y) is the center
                position, w the width, and h the height of the bounding box.

        Returns:
            (tuple[ndarray, ndarray]): Returns the measurement-corrected state distribution.
        """
        return super().update(mean, covariance, measurement)

initiate(measurement)

Create track from unassociated measurement.

Parameters:

Name Type Description Default
measurement ndarray

Bounding box coordinates (x, y, w, h) with center position (x, y), width, and height.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the mean vector (8 dimensional) and covariance matrix (8x8 dimensional) of the new track. Unobserved velocities are initialized to 0 mean.

Source code in ultralytics/trackers/utils/kalman_filter.py
def initiate(self, measurement: np.ndarray) -> tuple:
    """
    Create track from unassociated measurement.

    Args:
        measurement (ndarray): Bounding box coordinates (x, y, w, h) with center position (x, y), width, and height.

    Returns:
        (tuple[ndarray, ndarray]): Returns the mean vector (8 dimensional) and covariance matrix (8x8 dimensional)
            of the new track. Unobserved velocities are initialized to 0 mean.
    """
    mean_pos = measurement
    mean_vel = np.zeros_like(mean_pos)
    mean = np.r_[mean_pos, mean_vel]

    std = [
        2 * self._std_weight_position * measurement[2],
        2 * self._std_weight_position * measurement[3],
        2 * self._std_weight_position * measurement[2],
        2 * self._std_weight_position * measurement[3],
        10 * self._std_weight_velocity * measurement[2],
        10 * self._std_weight_velocity * measurement[3],
        10 * self._std_weight_velocity * measurement[2],
        10 * self._std_weight_velocity * measurement[3],
    ]
    covariance = np.diag(np.square(std))
    return mean, covariance

multi_predict(mean, covariance)

Run Kalman filter prediction step (Vectorized version).

Parameters:

Name Type Description Default
mean ndarray

The Nx8 dimensional mean matrix of the object states at the previous time step.

required
covariance ndarray

The Nx8x8 covariance matrix of the object states at the previous time step.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the mean vector and covariance matrix of the predicted state. Unobserved velocities are initialized to 0 mean.

Source code in ultralytics/trackers/utils/kalman_filter.py
def multi_predict(self, mean, covariance) -> tuple:
    """
    Run Kalman filter prediction step (Vectorized version).

    Args:
        mean (ndarray): The Nx8 dimensional mean matrix of the object states at the previous time step.
        covariance (ndarray): The Nx8x8 covariance matrix of the object states at the previous time step.

    Returns:
        (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
            velocities are initialized to 0 mean.
    """
    std_pos = [
        self._std_weight_position * mean[:, 2],
        self._std_weight_position * mean[:, 3],
        self._std_weight_position * mean[:, 2],
        self._std_weight_position * mean[:, 3],
    ]
    std_vel = [
        self._std_weight_velocity * mean[:, 2],
        self._std_weight_velocity * mean[:, 3],
        self._std_weight_velocity * mean[:, 2],
        self._std_weight_velocity * mean[:, 3],
    ]
    sqr = np.square(np.r_[std_pos, std_vel]).T

    motion_cov = [np.diag(sqr[i]) for i in range(len(mean))]
    motion_cov = np.asarray(motion_cov)

    mean = np.dot(mean, self._motion_mat.T)
    left = np.dot(self._motion_mat, covariance).transpose((1, 0, 2))
    covariance = np.dot(left, self._motion_mat.T) + motion_cov

    return mean, covariance

predict(mean, covariance)

Run Kalman filter prediction step.

Parameters:

Name Type Description Default
mean ndarray

The 8 dimensional mean vector of the object state at the previous time step.

required
covariance ndarray

The 8x8 dimensional covariance matrix of the object state at the previous time step.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the mean vector and covariance matrix of the predicted state. Unobserved velocities are initialized to 0 mean.

Source code in ultralytics/trackers/utils/kalman_filter.py
def predict(self, mean, covariance) -> tuple:
    """
    Run Kalman filter prediction step.

    Args:
        mean (ndarray): The 8 dimensional mean vector of the object state at the previous time step.
        covariance (ndarray): The 8x8 dimensional covariance matrix of the object state at the previous time step.

    Returns:
        (tuple[ndarray, ndarray]): Returns the mean vector and covariance matrix of the predicted state. Unobserved
            velocities are initialized to 0 mean.
    """
    std_pos = [
        self._std_weight_position * mean[2],
        self._std_weight_position * mean[3],
        self._std_weight_position * mean[2],
        self._std_weight_position * mean[3],
    ]
    std_vel = [
        self._std_weight_velocity * mean[2],
        self._std_weight_velocity * mean[3],
        self._std_weight_velocity * mean[2],
        self._std_weight_velocity * mean[3],
    ]
    motion_cov = np.diag(np.square(np.r_[std_pos, std_vel]))

    mean = np.dot(mean, self._motion_mat.T)
    covariance = np.linalg.multi_dot((self._motion_mat, covariance, self._motion_mat.T)) + motion_cov

    return mean, covariance

project(mean, covariance)

Project state distribution to measurement space.

Parameters:

Name Type Description Default
mean ndarray

The state's mean vector (8 dimensional array).

required
covariance ndarray

The state's covariance matrix (8x8 dimensional).

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the projected mean and covariance matrix of the given state estimate.

Source code in ultralytics/trackers/utils/kalman_filter.py
def project(self, mean, covariance) -> tuple:
    """
    Project state distribution to measurement space.

    Args:
        mean (ndarray): The state's mean vector (8 dimensional array).
        covariance (ndarray): The state's covariance matrix (8x8 dimensional).

    Returns:
        (tuple[ndarray, ndarray]): Returns the projected mean and covariance matrix of the given state estimate.
    """
    std = [
        self._std_weight_position * mean[2],
        self._std_weight_position * mean[3],
        self._std_weight_position * mean[2],
        self._std_weight_position * mean[3],
    ]
    innovation_cov = np.diag(np.square(std))

    mean = np.dot(self._update_mat, mean)
    covariance = np.linalg.multi_dot((self._update_mat, covariance, self._update_mat.T))
    return mean, covariance + innovation_cov

update(mean, covariance, measurement)

Run Kalman filter correction step.

Parameters:

Name Type Description Default
mean ndarray

The predicted state's mean vector (8 dimensional).

required
covariance ndarray

The state's covariance matrix (8x8 dimensional).

required
measurement ndarray

The 4 dimensional measurement vector (x, y, w, h), where (x, y) is the center position, w the width, and h the height of the bounding box.

required

Returns:

Type Description
tuple[ndarray, ndarray]

Returns the measurement-corrected state distribution.

Source code in ultralytics/trackers/utils/kalman_filter.py
def update(self, mean, covariance, measurement) -> tuple:
    """
    Run Kalman filter correction step.

    Args:
        mean (ndarray): The predicted state's mean vector (8 dimensional).
        covariance (ndarray): The state's covariance matrix (8x8 dimensional).
        measurement (ndarray): The 4 dimensional measurement vector (x, y, w, h), where (x, y) is the center
            position, w the width, and h the height of the bounding box.

    Returns:
        (tuple[ndarray, ndarray]): Returns the measurement-corrected state distribution.
    """
    return super().update(mean, covariance, measurement)





Created 2023-11-12, Updated 2023-11-25
Authors: glenn-jocher (3)