Monocular rear approach indicator for motorcycles

Conventional rear-view mirrors on motorcycles only allow a limited visibility as they are shaky and cover a small field of view. Especially at high speeds with strong headwind, it is difficult for the rider to turn his head to observe blind spots. To support the rider in observing the rear and blind-spots, a monocular system that indicates approaching vehicles is proposed in this paper. The vision based indication relies on sparse optical flow estimation. In a first step, a rough separation of background and approaching object pixel motion is done in an efficient and computationally cheap way. In a post-processing step, pixel motion information is further checked on geometric meaningful transformations and continuity over time. As a prototype, the system has been mounted on a Honda Pan-European motorcycle plus monitor in the dashboard that shows the rear-view image to the rider. If an approaching object is detected, the rider gets an indication on the monitor. The rear-view on the monitor not only acts as HMI (Human Machine Interface) for the indication, but also significantly extends the visibility compared to mirrors. The algorithm has been extensively evaluated for relative speeds from 20 km/h to 100 km/h (speed differences between motorcycle and approaching vehicle), at normal, rainy and night conditions. Results show that the approach offers a sensing range from 20 m at low speed up to 60 m at night.