Method and system for measuring vehicle speed based on movement of video camera

• US 8,269,833 B2
• Filed: 12/08/2009
• Issued: 09/18/2012
• Est. Priority Date: 03/10/2009
• Status: Active Grant

• Current Assignee: Topcon Positioning Systems Incorporated (Topcon Corporation)
• Original Assignee: Topcon Positioning Systems Incorporated (Topcon Corporation)
• Inventors: Vorobiev, Michael Y.
• Primary Examiner(s): Ustaris, Joseph
• Assistant Examiner(s): Holder, Anner
• Application Number:
  US12/989,424
• Publication Number:
  US 20120026329A1
• Time in Patent Office: 1,015 Days
• Field of Search: 348/148, 382/104
• US Class Current: 348/148
• CPC Class Codes: B60T 2250/04 Vehicle reference speed; Vehicle body speed
• CPC Class Codes: G01C 21/12 executed aboard the object being navigated; Dead reckoning
• CPC Class Codes: G01P 3/38 using photographic means
• CPC Class Codes: G01S 11/12 using electromagnetic waves other than radio waves
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/30252 Vehicle exterior; Vicinity of vehicle
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51

Abstract

A digital video camera is placed on a vehicle. The video camera is attached to the vehicle and is directed to a surface at a certain angle to the surface. The camera angle can change while vehicle is in motion. The camera angle is constantly measured by angular sensor (i.e., inclinometer). Images of the surface are projected onto a video matrix and transformed into a sequence of digital frames that are formed at a pre-set time interval. A speed of the video camera relative to the surface is calculated as a ratio of an off-set between the adjacent frames and the time interval between the frames. Then a known relative speed of the vehicle can be corrected by multiplication of the height of the camera (above the surface) by a coefficient that equals a ratio of the known vehicle speed and the measured camera speed.

Claims

1. A method for measuring movement of a video camera placed on a moving vehicle, the method comprising:

(a) acquiring, by the video camera, a video data of the earth surface;

(b) transforming the video data into a sequence of digital frames;

(c) correcting perspective distortions of each digital frame;

(d) finding a correlation of adjacent frames, wherein frame images have maximum coincidence; and

(e) measuring off-set value between the adjacent frames,

wherein;

time intervals between the adjacent frames are measured;

camera angle, camera field of view and camera height above the earth surface are recorded at a time of generation of each frame;

a simplified image frame is created for each image frame by approximation and filtering of the image frame;

perspective distortions are corrected for each simplified image frame based on the camera angle, the camera field of view and the camera height above the surface;

correlation of adjacent simplified frames, wherein frame images having maximum coincidence are found;

correction off-set value is calculated based on changes in the camera angle during generation of the image frames corresponding to the simplified image frames; and

an actual off-set of portion of the surface is calculated based on the off-set of the adjacent simplified image frames corrected by the correction off-set value.

2. The method of claim 1, wherein the simplified image frames are generated by transforming a color image into a monotone grey scale image.

3. The method of claim 1, wherein the simplified image frames are generated by transforming a color image into a monotone color image.

4. The method of claim 1, wherein the simplified image frames are generated by transforming a monotone grey scale image pixel-by-pixel into a binary image by comparing brightness values of all pixels against a pre-set threshold value.

5. The method of claim 1, wherein the simplified image frames are generated by transforming an infra-red image into a monotone grey scale image.

6. The method of claim 1, wherein spherical aberration is corrected on the image frames prior to generation of the simplified image frames.

7. The method of claim 1, wherein the video camera is calibrated by using a calibration table and correction coefficients for spherical aberration are determined.

8. The method of claim 1, wherein portions of the adjacent simplified image frames are used, wherein the portions have the same number and the same positioning of pixels.

9. The method of claim 1, wherein the finding of the correlation of the adjacent frames beginning from third is performed in neighborhood area of a point of maximum coincidence of images within the adjacent image frames.

10. The method of claim 1, wherein the maximum correlation of the adjacent simplified frames is calculated by using an approximation function and by finding a correlation peak of this function.

11. The method of claim 10, wherein the approximation function is a parabolic function.

12. The method of claim 1, wherein the finding of the correlation of the adjacent simplified frames includes determining correlation of angles of the simplified frames having maximally coincident images.

13. The method of claim 1, further comprising calculating a current speed of the camera relative to the surface as a ratio of the off-set between the simplified image frames and the time interval between the image frames corresponding to the simplified image frames.

14. The method of claim 1, further comprising correcting the camera height above the surface value by multiplying this value by a ratio of known vehicle speed and a measured speed.

15. The method of claim 1, wherein the off-set of the camera is calculated as a sum of the off-sets between pairs of the adjacent simplified image frames.

16. A system for measuring movement of a vehicle, the system comprising:

a video camera placed on the vehicle for generating digital images of an earth surface, wherein the video camera changes its angle relative to the earth surface as the vehicle moves over the earth surface;

a processing unit connected to the camera for processing video image data; and

a device for measuring camera angles relative to the earth surface, wherein the processing unit approximates and filters the video image data and calculates off-sets of earth surface images caused by changes in the camera angles relative to the earth surface, and

wherein;

time intervals between adjacent frames are measured;

a camera angle, a camera field of view and a camera height above the earth surface are recorded at a time of generation of each frame;

a simplified image frame is created for each image frame by approximation and filtering of the image frame;

perspective distortions are corrected for each simplified image frame based on the camera angle, the camera field of view and the camera height above the surface;

correlations of adjacent simplified frames, wherein frame images having maximum coincidence, are found;

a correction off-set value is calculated based on changes in the camera angle during generation of the image frames corresponding to the simplified image frames; and

an actual off-set of a portion of the surface is calculated based on the off-set of the adjacent simplified image frames corrected by the correction off-set value.