SpeedTrap (Insert better title image) Mike Burns Christopher DeCoro Ananya Misra What is SpeedTrap? • Optical version of police radar speed detectors • Uses traffic video cameras to determine vehicle speed • Immune to jamming and detection System Components • Camera Calibration • Background Detection • Vehicle Tracking Camera Calibration • Map Screen pixel distance to real-world units • Determine locations of lanes • Assign regions of interest • Assumptions: – Road is flat (all points lie on a plane) – Road is straight – Occlusions are minimized • Our system requires measurement of 4 points in space – These form a quadrilateral in screen space, rectangle in road space – Only relative distances are needed Camera Calibration Procedure 1. Click on 4 points in space 2. Click on center of each lane 3. For each lane, click on start and end of region of interest • Accuracy is important for Step 1, less so for Steps 2 & 3 Camera Calibration Algorithm • Goal: compute the projective matrix mapping screen space to “road space” A B D E G H C a x F a y 1 1 bx cx by 1 cy 1 d x 0 w w 0 d y 0 0 h h 1 1 1 1 1 • Road space is measured in real world units (feet) • Corresponds to position in the plane of road • Values w, h are given as dimensions in road space • Vectors a, b, c, d are 4 points in screen space • Values A-H are unknown Camera Calibration Algorithm • Use least squares to compute affine matrix (G, H = 0) • Use iterative optimization to refine to a projective matrix • Map screen points for each lane into road space Background Detection • Goal: Determine which pixels belong to cars • Simplifies the task of tracking individual cars • Measure variance to identify mean road image • Compare frame to road image to get car mask • Perform median filtering to smooth mask Tracking • Goal: Track individual cars and compute speeds • Must recognize new cars, and track existing ones • Scan a “region of interest”, or line segment in road space • Near beginning of ROI, changes indicate new car • Follow blob in ROI across frames, indicating speed