Vehicle speed estimation from two images for LIDAR second assessment

Vehicle speed control has been traditionally carried out by RADAR and more recently by LIDAR systems. We present a solution that derives the speed from two images acquired by a static camera and one real dimension from the vehicle. It was designed to serve the purpose of second assessment in case of legal dispute about a LIDAR speed measure. The approach follows a stereo paradigm, considering the equivalent problem of a stationary vehicle captured by a moving camera. 3D coordinates of vehicle points are obtained as the intersection of 3D lines emanating from corresponding points in both images, using the camera pinhole model. The displacement, approximated by a translation, is derived from the best match of reconstructed 3D points, minimising the residual error of 3D line intersection and the deviation with the known dimensions of the licence plate. A graphical interface lets the user select and refine vehicle points, starting with the 4 corners of the licence plate. The plate dimension is selected from a list or typed in. More than 100 speed estimation results confirmed hypothesis about the translation approximation and showed a maximal deviation with LIDAR speed of less than +/- 10 % as required by the application.