Method and apparatus for monitoring traffic flow

• US 5,296,852 A
• Filed: 02/27/1991
• Issued: 03/22/1994
• Est. Priority Date: 02/27/1991
• Status: Expired due to Fees

• Current Assignee: Rajendra P. Rathi
• Original Assignee: Rajendra P. Rathi
• Inventors: Rathi, Rajendra P.
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): Tong, Nina
• Application Number:
  US07/661,297
• Time in Patent Office: 1,119 Days
• Field of Search: 340/933, 340/934, 340/937, 340/939, 358/105, 358/108, 364/436
• US Class Current: 340/933
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors

Abstract

A vision processing apparatus and method for detecting and monitoring traffic flow. The method includes the steps of generating successive images of a section of roadway; transducing the successive images into successive arrays of pixels, each pixel having a luminance value associated therewith; summing the luminance values of all pixels contained within a subarray, or "window" in each one of the arrays; comparing the pixel luminance sum for each one of the subarrays to a reference value; and generating data indicative of the presence of traffic in the section of the path when the difference between the pixel luminance sum and the reference value exceeds a predetermined value. The generated data can thereafter be analyzed to determine various traffic and vehicle parameters, or can be used to operate traffic control devices.

Claims

1. A method for determining the speed of a vehicle traveling along a predetermined path, comprising the steps of:

generating a reference image of a section of said path;

transducing said reference image into a reference array of pixels;

generating successive images of said section of said path;

transducing said successive images into successive arrays of pixels;

separating each one of said arrays of pixels into first and second subarrays of pixels, each of said subarrays corresponding to first and second portions of said path, said first and second portions of said path being separated by a known distance;

summing the intensity values of all the pixels in said first subarray of said reference array;

summing the intensity values of all the pixels in said first subarray of each one of said successive arrays;

successively comparing the pixel intensity sum for each said first subarray of each one of said successive arrays to the pixel intensity sum for said first subarray of said reference array;

generating data indicative of the presence of said vehicle in said first portion of said path when the difference in pixel intensity sums between said first subarrays recited in said comparing step exceeds a predetermined value;

recording a first reference time when said vehicle is first determined to be present in said first portion of said path;

summing the intensity values of all the pixels in said second subarray of said reference array;

summing the intensity values of all the pixels in said second subarray of each one of said successive arrays;

successively comparing the pixel intensity sum for each said second subarray of each one of said successive arrays to the pixel intensity sum for said second subarray of said reference array;

generating data indicative of the presence of said vehicle in said second portion of said path when the difference in pixel intensity between said second subarrays recited in said last-recited comparing step exceeds said predetermined value;

recording a second reference time when said vehicle is first determined to be present in said second portion of said path; and

calculating the speed of said vehicle from the difference in said first and second reference times and said known distance between said first and second portions of said path.

2. A method for determining the interval between first and second vehicles traveling along a predetermined path, comprising the steps of:

generating a reference image of a section of said path;

transducing said reference image into a reference array of pixels;

generating successive images of said section of said path;

transducing said successive images into successive arrays of pixels;

successively comparing pixel intensity information obtained from each one of said successive arrays to pixel intensity information obtained from said reference array;

generating data indicative of the presence of said first vehicle in said section of said path when the difference in pixel intensity information between one of said successive arrays and said reference array exceeds a predetermined value;

recording a first reference time when said first vehicle is determined to be present in said section of said path;

generating data indicative of the presence of said second vehicle in said section of said path when the difference in pixel intensity information between a second one of said successive arrays and said reference array exceeds said predetermined value;

recording a second reference time when said second vehicle is determined to be present in said section of said path; and

calculating the interval between said first and second vehicles from the difference in said first and second reference times.

3. A method for determining the length of a vehicle traveling along a predetermined path, comprising the steps of:

generating a first reference image of a first section of said path;

transducing said first reference image into a first reference array of pixels;

generating first successive images of said first section of said path;

transducing said successive images into first successive arrays of pixels;

successively comparing pixel intensity information obtained from each one of said first successive arrays to pixel intensity information obtained from said first reference array;

generating data indicative of the presence of said vehicle in said first section of said path when the difference in pixel intensity information between one of said first successive arrays and said first reference array exceeds a first predetermined value;

recording a first reference time when said vehicle is determined to be present in said first section of said path;

generating data indicating that said vehicle has vacated said first section of said path when the difference in pixel intensity information between one of said first successive arrays and said first reference array falls below a second predetermined value;

recording a second reference time when said vehicle is determined to have vacated said first section of said path;

determining the difference between said first and second reference times;

determining the speed of said vehicle; and

determining the length of said vehicle by multiplying said time difference by the speed of said vehicle.

4. The method according to claim 3, wherein the step of determining the speed of said vehicle comprises the steps of:

generating a second reference image of a second section of said path, said first and second sections being separated by a known distance;

transducing said second reference image into a second reference array of pixels;

generating second successive images of said second section of said path;

transducing said second successive images of said second section of said path into second successive arrays of pixels;

successively comparing pixel intensity information obtained from said second successive arrays to pixel intensity information obtained from said second reference array;

generating data indicative of the presence of said vehicle in said second section of said path when the difference in pixel intensity information between one of said second successive arrays and said second reference array exceeds said first predetermined value;

recording a third reference time when said vehicle is first determined to be present in said second section of said path;

determining the speed of said vehicle from the difference in said first and third reference times and said known distance between said first and second sections of said path.

5. The method according to claim 3, further comprising the step of classifying vehicle types by length.

6. A method for tracking the movement of a vehicle within the field of view of a video camera, comprising the steps of:

generating successive images of said field of view;

transducing said successive images into successive arrays of pixels;

identifying the coordinates of pixels associated with the image of said vehicle for each of said successive arrays;

electronically determining the centroid of the image of said vehicle from said coordinates; and

recording the coordinates of said centroid for each of said successive arrays.

7. The method according to claim 6, further comprising the step of recording time of occurrence together with the coordinates of said centroid for each of said arrays.

8. The method according to claim 7, further comprising the step of determining vehicle velocity from said recorded coordinate and time data.

9. The method according to claim 7, further comprising the step of determining vehicle acceleration from said recorded coordinate and time data.