F2008-08-041
Dynamic Stereo Vision for Intersection Assistance
More than one third of all traffic accidents with injuries occur in urban areas, especially at intersections. Therefore, a driver assistance system supporting the driver in cities is highly desirable and has a tremendous potential of reducing the number of collisions at intersections.
A suitable system for such complex situations requires a comprehensive understanding of the scene. This implies a precise estimation of the free space and the reliable detection and tracking of other moving traffic participants. Since the goal of accident free traffic requires a sensor with high spatial and temporal resolution, stereo vision will play an important role in future driver assistance systems.
Most known stereo systems concentrate on single image pairs. However, in intelligent vehicles applications image sequences have to be analyzed. The contribution shows that a smart fusion of stereo vision and motion analysis (optical flow) gives much better results than classical frame-by-frame reconstructions. The basic idea is to track points with depth known from stereo vision over two and more consecutive frames and to fuse the spatial and temporal information using Kalman filters. The result is an improved accuracy of the 3D-position and an estimation of the 3D-motion of the considered point at the same time. This approach, called 6D Vision, enables a detection of moving objects even if they are partially hidden.
From static points very accurate occupancy grids are built. A global optimization technique delivers a robust estimation of the free space which is important for the situation analysis. The moving pixels are clustered to objects which are than tracked over time in order to estimate their motion state and to predict their paths. This allows for powerful collision avoidance systems: pedestrians crossing the street are detected before they enter the lane; the same holds for vehicles from the side which are not detectable by common radar systems. Since we are able to estimate the yaw rate of oncoming traffic, the prediction is not restricted to straight motion but can detect potential collisions with turning traffic, especially at intersections.
Urban vision asks for a large sensor angle. A former system used map information in order to guide a turnable platform. Within the German project AKTIV a fisheye stereo camera system is under development that allows vision angles up to 150 degrees. If the 6D-Vision principle is applied to these images, vehicles coming from the side are visible, too.
The system runs in real-time on a standard Pentium IV processor and is under test in daily traffic.
Session: Occupant & Pedestrian Protection I