Interpretation of deepsort source code (V)

deepsort Project address

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Catalog
deepsort Principle and analysis summary

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nn_matching.py

# vim: expandtab:ts=4:sw=4
import numpy as np


def _pdist(a, b):
    """Compute pair-wise squared distance between points in `a` and `b`.

    Parameters
    ----------
    a : array_like
        An NxM matrix of N samples of dimensionality M.
    b : array_like
        An LxM matrix of L samples of dimensionality M.

    Returns
    -------
    ndarray
        Returns a matrix of size len(a), len(b) such that eleement (i, j)
        contains the squared distance between `a[i]` and `b[j]`.

    """
    a, b = np.asarray(a), np.asarray(b)
    if len(a) == 0 or len(b) == 0:
        return np.zeros((len(a), len(b)))
    a2, b2 = np.square(a).sum(axis=1), np.square(b).sum(axis=1)
    r2 = -2. * np.dot(a, b.T) + a2[:, None] + b2[None, :]
    r2 = np.clip(r2, 0., float(np.inf))
    return r2


#  Calculate the cosine distance 
def _cosine_distance(a, b, data_is_normalized=False):
    """Compute pair-wise cosine distance between points in `a` and `b`.

    Parameters
    ----------
    a : array_like
        An NxM matrix of N samples of dimensionality M.
    b : array_like
        An LxM matrix of L samples of dimensionality M.
    data_is_normalized : Optional[bool]
        If True, assumes rows in a and b are unit length vectors.
        Otherwise, a and b are explicitly normalized to lenght 1.

    Returns
    -------
    ndarray
        Returns a matrix of size len(a), len(b) such that eleement (i, j)
        contains the squared distance between `a[i]` and `b[j]`.

    """
    if not data_is_normalized:
        a = np.asarray(a) / np.linalg.norm(a, axis=1, keepdims=True)
        b = np.asarray(b) / np.linalg.norm(b, axis=1, keepdims=True)
    return 1. - np.dot(a, b.T)


#  Calculate Euclidean distance 
def _nn_euclidean_distance(x, y):
    """ Helper function for nearest neighbor distance metric (Euclidean).

    Parameters
    ----------
    x : ndarray
        A matrix of N row-vectors (sample points).
    y : ndarray
        A matrix of M row-vectors (query points).

    Returns
    -------
    ndarray
        A vector of length M that contains for each entry in `y` the
        smallest Euclidean distance to a sample in `x`.

    """
    distances = _pdist(x, y)
    return np.maximum(0.0, distances.min(axis=0))


def _nn_cosine_distance(x, y):
    """ Helper function for nearest neighbor distance metric (cosine).

    Parameters
    ----------
    x : ndarray
        A matrix of N row-vectors (sample points).
    y : ndarray
        A matrix of M row-vectors (query points).

    Returns
    -------
    ndarray
        A vector of length M that contains for each entry in `y` the
        smallest cosine distance to a sample in `x`.

    """
    distances = _cosine_distance(x, y)
    return distances.min(axis=0)


#  Nearest neighbor distance measurement class 
class NearestNeighborDistanceMetric(object):
    """
    A nearest neighbor distance metric that, for each target, returns
    the closest distance to any sample that has been observed so far.

    Parameters
    ----------
    metric : str
        Either "euclidean" or "cosine".
    matching_threshold: float
        The matching threshold. Samples with larger distance are considered an
        invalid match.
    budget : Optional[int]
        If not None, fix samples per class to at most this number. Removes
        the oldest samples when the budget is reached.

    Attributes
    ----------
    samples : Dict[int -> List[ndarray]]
        A dictionary that maps from target identities to the list of samples
        that have been observed so far.

    """

    def __init__(self, metric, matching_threshold, budget=None):

        #  Use nearest neighbor Euclidean distance 
        if metric == "euclidean":
            self._metric = _nn_euclidean_distance
        #  Use nearest neighbor cosine distance 
        elif metric == "cosine":
            self._metric = _nn_cosine_distance
        else:
            raise ValueError(
                "Invalid metric; must be either 'euclidean' or 'cosine'")
        #  Call , Maximum cosine distance 
        self.matching_threshold = matching_threshold
        # budge  The budget , control feature The amount of 
        self.budget = budget
        # samples It's a dictionary {
      id->feature list}
        self.samples = {
    }

    #   The function of this method is to adjust the dictionary of stored features so that the stored features are in the state of confirmed The object of 
    #   effect ： Partial fit , Update the measured distance with new data 
    def partial_fit(self, features, targets, active_targets):
        """Update the distance metric with new data.

        Parameters
        ----------
        features : ndarray
            An NxM matrix of N features of dimensionality M.
        targets : ndarray
            An integer array of associated target identities.
        active_targets : List[int]
            A list of targets that are currently present in the scene.

        """
        # activate_targets： Status as confirmed Tracking object of 
        # targets and features Yes, all current status is confirmed Of the tracking object id And characteristics 
        for feature, target in zip(features, targets):
            # setdefault The way is if this is not in the dictionary target Join in , Yes, no u operation 
            self.samples.setdefault(target, []).append(feature)
            #  Set budget , How many targets can each class have at most , If it exceeds, keep the latest budget features 
            if self.budget is not None:
                self.samples[target] = self.samples[target][-self.budget:]
        #  Filter active targets 
        self.samples = {
    k: self.samples[k] for k in active_targets}

    #  effect ： Compare feature and targets Distance between , Return a cost matrix 
    def distance(self, features, targets):
        """Compute distance between features and targets.

        Parameters
        ----------
        features : ndarray
            An NxM matrix of N features of dimensionality M.
        targets : List[int]
            A list of targets to match the given `features` against.

        Returns
        -------
        ndarray
            Returns a cost matrix of shape len(targets), len(features), where
            element (i, j) contains the closest squared distance between
            `targets[i]` and `features[j]`.

        """
        cost_matrix = np.zeros((len(targets), len(features)))
        #  Calculate each track And detection The generation value of , Row representation track
        for i, target in enumerate(targets):
            cost_matrix[i, :] = self._metric(self.samples[target], features)
        return cost_matrix