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