Count line crossings🔗

Counts the number of times a trajectory or a set of trajectories crosses a line segment. The tool considers only the end of a trajectory; a crossing will be counted only if the last point of a trajectory is the first one on that side of the detection line.

The tool makes a distinction between positive and negative crossing direction. If you think of the line segment as the X axis of a right-handed coordinate system, positive and negative directions are defined by the direction of the Y axis. That is, if the line segment points up, positive direction is to the right.


  • trajectories: A trajectory or a set of trajectories represented as an N-by-2 matrix. If there is only one trajectory, both outputs will be either 0 or 1.

  • blockSize: If the input contains multiple trajectories, this matrix stores the number of points in each. An M-by-1 integer matrix in which the number of rows (M) corresponds to the number of detected trajectories.

  • identifiers: A (temporarily) unique identifier for each trajectory. An M-by-1 integer matrix containing an auto-generated unique ID for each trajectory.

  • startPoint: The location of the start of a line segment.

  • endPoint: The location of the end of a line segment.

  • width: The width of the detection line. A non-zero width can be used as a hysteresis: a crossing will be detected only if a trajectory crosses two lines that are width units apart.


  • positiveCrossings: The number of crossings to the positive direction.

  • positiveIdentifiers: Identifiers of those trajectories which made a positive crossing.

  • negativeCrossings: The number of crossings to the negative direction.

  • negativeIdentifiers: Identifiers of those trajectories which made a negative crossing.