A complete prototype system for measuring vehicle lateral position has been set up during the course of this master's thesis project. In the development of the software, images acquired from a backward-looking video camera mounted on the roof of the vehicle were used. The problem of using computer vision to measure lateral position can be divided into road marking detection and lateral position extraction. Since the strongest characteristic of a road marking image are the edges of the road markings, the road marking detection step is based on edge detection. For the detection of the straight edge lines a Hough based method was chosen. Due to peak spreading in Hough space, the difficulty of detecting the correct peak in Hough space was encountered. A flexible Hough peak detection algorithm was developed based on an adaptive window that takes peak spreading into account. The road marking candidate found by the system is verified before the lateral position data is generated. A good performance of the road marking tracking algorithm was obtained by exploiting temporal correlation to update a search region within the image. A camera calibration made the extraction of real-world lateral position information and yaw angle data possible. This vision-based method proved to be very accurate. The standard deviation of the error in the position detection is 0.012 m within an operating range of +-2 m from the image centre. During continuous road markings the rate of valid data is on average 96 per cent, whereas it drops to around 56 per cent for sections with intermittent road markings. The system performs well during lane change manoeuvres, which is an indication that the system tracks the correct road marking. This prototype system is a robust and automatic measurement system, which will benefit VTI in its many driving behaviour research programs. (Author/publisher) An electronic version of this publication is available at http://www.ep.liu.se/exjobb/isy/2003/3417/
Samenvatting