Deriving camera and lens settings for fixed traffic enforcement and ALPR cameras

A methodology for computing parameters of fixed ALPR and traffic enforcement cameras is presented. The minimum spatial resolution of the camera is defined on the basis of license plate font analysis. A camera calibration model is used to measure dimensions of the area of interest. The camera pose is analyzed with the objective of minimizing occlusion and maximizing the number of frames containing the infringing vehicle. The optimal focal length of the lens is computed based on the scene and sensor dimensions. The lens aperture is set in a way that optimizes the sharpness and brightness of license plates in the area of interest. The minimum shutter speed is defined in order to cope with fast moving vehicles. This approach has been confirmed in practice in configuring the traffic enforcement system of the city of Belgrade.