Vehicle speed monitoring system
First Claim
Patent Images
1. A method for determining a vehicle'"'"'s speed within a traffic lane, the method to be used with a camera including a lens and a viewing field that generates images of the vehicle within the camera'"'"'s viewing field, the method comprising the steps of:
- generating first and second images of the vehicle while at least one feature of the vehicle is in the viewing field, the one feature being a reference point on the vehicle, the second image following the first image by a known time period;
determining the feature positions in the first and second images;
converting the first and second image feature positions to actual positions within the traffic lane to compensate for non-linearities; and
mathematically combining the first and second actual positions and the known time period to determine a precise vehicle speed.
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Abstract
A method for determining the speed of a vehicle using a camera. The method automatically compensates an apparent speed determination for inaccuracies due to the position of the camera with respect to the vehicle. The invention also includes a method for calibrating a camera to compensate for inaccuracies due to the position of the camera.
338 Citations
36 Claims
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1. A method for determining a vehicle'"'"'s speed within a traffic lane, the method to be used with a camera including a lens and a viewing field that generates images of the vehicle within the camera'"'"'s viewing field, the method comprising the steps of:
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generating first and second images of the vehicle while at least one feature of the vehicle is in the viewing field, the one feature being a reference point on the vehicle, the second image following the first image by a known time period; determining the feature positions in the first and second images; converting the first and second image feature positions to actual positions within the traffic lane to compensate for non-linearities; and mathematically combining the first and second actual positions and the known time period to determine a precise vehicle speed. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22)
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23. A method for calibrating a system used to determine the speed of a vehicle passing through a viewing field defined by a viewing field angle ω
- , the system including a camera having a lens positioned a height H above a traffic lane and the lens in a horizontal lens plane angled at least partially downwardly so that a line between the lens and the center of the viewing field defines a known inclination angle I below the lens plane, the method for determining an actual viewing field angle and the actual lens height, the method used with a computer that includes dimension data for at least one dimensioned feature and feature height data for at least two features of different heights of a reference vehicle, the method comprising the steps of;
(a) assuming initial lens height H, inclination angle I and viewing field angle ω
approximations where the initial inclination angle is the known inclination angle;(b) identifying specific sequential images containing the passing of a reference vehicle through the viewing field, sequential images acquired at known time intervals, the reference vehicle including the dimensioned feature and the at least two reference vehicle features of known and different heights; (c) identifying reference images from the specific sequential images wherein at least one reference image contains the dimensioned feature, at least two images contain the first feature of known height, and at least two images contain the second feature of known height; (d) determining the apparent displacement of the first feature of known height between the images in which the first feature appears and determining the apparent displacement of the second feature of known height between the images in which the second feature appears; (e) calculating a new camera height approximation based on the apparent displacements of the features of known heights; (f) comparing the apparent and actual dimensioned feature dimensions and, where the apparent dimension is larger than the actual dimension and not within a predetermined range; (i) reducing the initial viewing field angle approximation by a predetermined amount and reducing the predetermined amount; and where the apparent dimension is smaller than the actual dimension and not within the predetermined range; (ii) increasing the initial viewing field angle approximation by a predetermined amount and reducing the predetermined amount; (g) re-determining the apparent dimensioned feature dimension with the new viewing field angle; (h) where the apparent dimension is not within the predetermined range of the actual dimension, repeating steps f and g; (i) determining the difference between the initial and the new viewing field angle approximations and the difference between the initial and the new height approximations and, where the differences are below a predetermined magnitude, skipping to step k; (j) repeating steps a through i with the new height approximation as the initial height approximation and the new viewing angle approximation as the initial approximation; and (k) storing the new height approximation and the new viewing field angle approximation for use in determining vehicle speed. - View Dependent Claims (24, 25, 26, 27, 28, 29, 30, 31)
- , the system including a camera having a lens positioned a height H above a traffic lane and the lens in a horizontal lens plane angled at least partially downwardly so that a line between the lens and the center of the viewing field defines a known inclination angle I below the lens plane, the method for determining an actual viewing field angle and the actual lens height, the method used with a computer that includes dimension data for at least one dimensioned feature and feature height data for at least two features of different heights of a reference vehicle, the method comprising the steps of;
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32. A method for calibrating a camera and computer system used to determine the speed of a vehicle passing through a viewing field defined by a camera viewing field angle ω
- , the system including a camera having a lens positioned a height H above a traffic lane and the lens in a horizontal lens plane angled at least partially downwardly so that a line between the lens and the center of the viewing field defines a known inclination angle I below the lens plane, the method comprising the steps of;
(i) measuring the inclination angle I; (ii) determining the actual camera height H and an optimal viewing field angle ω
;(iii) adjusting the camera so as to provide the optimal viewing field angle; and (iv) providing software code that compensates for image distortion due to the viewing field angle, the inclination angle and the camera height. - View Dependent Claims (33, 34, 35, 36)
- , the system including a camera having a lens positioned a height H above a traffic lane and the lens in a horizontal lens plane angled at least partially downwardly so that a line between the lens and the center of the viewing field defines a known inclination angle I below the lens plane, the method comprising the steps of;
Specification