Automatic Traffic Monitoring from an Airborne Wide Angle Camera System

We present an automatic traffic monitoring approach using data of an airborne wide angle camera system. This camera, namely the “3K-Camera”, was recently developed at the German Aerospace Center (DLR). It has a coverage of 8 km perpendicular to the flight direction at a flight height of 3000 m with a resolution of 45 cm and is capable to take images at a frame rate of up to 3 fps. Based on georeferenced images obtained from this camera system, a near real-time processing chain containing road extraction, vehicle detection, and vehicle tracking was developed and tested. The road extraction algorithms handle a-priori information provided by a road database for a first guess of the location of the roads. Two different techniques can be used for road extraction. In the first method, roadside features are found by using an edge detector based on ISEF filtering, selecting the steepest edge, which is normally the edge between the tarry roads and the vegetation. The second method extracts roads by searching the roadside markings using a dynamical threshold operator and a line detector. Vehicle detection then is limited to the road areas found by the road extraction algorithms. It is based on an edge detector, a k-means clustering of the edges, and on geometrical constraints, e.g. vehicle size. Vehicle tracking is performed by matching detected vehicles in pairs of consecutive images. For this matching the normalized cross correlation is calculated for each detected car within a limited search area. The algorithms for road extraction, vehicle detection and vehicle tracking proved to be quite sophisticated, enabling car detection and tracking rates with a completeness of 70 % and a correctness of up to 90 % on images obtained from a flight height of 1000 m.