Kalman

A constant-velocity Kalman filter over a 2D point — the smoother behind ObjectTracker, useful on its own to steady a jittery detection or to coast through a frame where the measurement dropped out.

The state is position and velocity (x, y, vx, vy); you predict the next position, then correct it with a fresh measurement (or skip the correction if you have none this frame and trust the model). Owns a native filter — caller-owned, close it. Stateful and not safe to share across threads; give each thread its own, as with the detectors.