Method and apparatus for calibrating three-dimensional space for machine vision applications

• US 5,473,931 A
• Filed: 04/14/1995
• Issued: 12/12/1995
• Est. Priority Date: 07/22/1993
• Status: Expired due to Fees

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Rodriguez, Alex, Cerny, Darin G., Brady, Mark J.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): LARKIN, DANIEL SEAN
• Application Number:
  US08/422,579
• Time in Patent Office: 242 Days
• Field of Search: 73/1 D, 340/933, 340/934, 340/937, 340/942, 364/436, 364/438, 364/560, 364/561, 364/571.01, 348/135-137, 348/140-142, 348/148, 348/149, 348/169
• US Class Current: 73/1.75
• CPC Class Codes: G01B 11/022 by means of tv-camera scanning
• CPC Class Codes: G01P 21/02 of speedometers
• CPC Class Codes: G08G 1/04 using optical or ultrasonic detectors

Abstract

A calibration apparatus for calibrating three-dimensional space for a machine vision system and a method for using the calibration apparatus for calibrating the machine vision system are disclosed. The calibration apparatus comprises pairs of indicators, such as lights, mounted on a frame, each pair of lights separated by a known horizontal distance. The calibration apparatus may be mounted on the back of a vehicle that moves the apparatus through a roadway scene at a known speed. A machine vision system tracks the calibration apparatus, specifically the pairs of lights mounted on the frame, and maps the pixel space of the machine vision system to three-dimensional space.

Claims

1. A system for calibrating a three-dimensional space, said system for use with a machine vision system, said system comprising:

a) a frame;

b) at least one pair of indicators mounted on said frame;

c) movement means for moving said frame through said three-dimensional space at a known constant speed;

d) means for tracking said at least one pair of indicators through said three-dimensional space; and

e) means for mapping pixel space to said three-dimensional space based on the location of said at least one pair of indicators within said pixel space and said known, constant speed of said at least one pair of indicators, thereby calibrating said three-dimensional space.

2. The apparatus for calibrating a three-dimensional space according to claim 1, wherein said at least one pair of indicators comprises at least one pair of lights.

3. The apparatus for calibrating a three-dimensional space according to claim 1, wherein said at least one pair of indicators comprises a plurality of pairs indicators, said pairs of indicators horizontally spaced apart at a constant width, each pair of indicators located on different vertical planes.

4. The apparatus for calibrating a three-dimensional space according to claim 3, wherein said indicators are located on different vertical planes based on different vehicle classes.

5. The apparatus for calibrating a three-dimensional space according to claim 1, wherein said movement means comprises a vehicle.

6. The apparatus for calibrating a three-dimensional space according to claim 1, wherein said frame is a collapsible frame.

7. The apparatus for calibrating a three-dimensional space according to claim 1, wherein said at least one pair of indicators are adjustably mounted onto said frame.

8. The system for calibrating a three-dimensional space according to claim 1, wherein said means for tracking includes means for acquiring video images, said video images comprising a plurality of video frames with images of said at least one pair of indicators taken at constant intervals.

9. The system for calibrating a three-dimensional space according to claim 8, further comprising a memory having memory locations, wherein said at least one pair of indicators are spaced apart by a known real-world horizontal distance and wherein said means for mapping comprises:

a) means for determining a first pair of pixel coordinates and a second pair of pixel coordinates for each pair of indicators within said acquired video images, said first and second pair of pixel coordinates having a horizontal coordinate and a vertical coordinate;

b) means for determining a total real-world distance said at least one pair of indicators has moved in the vertical pixel direction; and

c) means for determining a ratio of said known real-world horizontal distance between said pair of indicators to the difference of said first and second horizontal pixel coordinates, said ratio determined for each said pair of indicators in each said video frame;

d) means for storing said ratios, said total real-world distances said at least one pair of indicators has moved, and said horizontal coordinates for each said vertical coordinate in said memory locations.

10. The system for calibrating a three-dimensional space according to claim 9, wherein said at least one pair of indicators comprises a plurality of pairs of indicators and wherein said means for mapping further comprises:

a) means for interpolating between said ratios and said total real-world distances moved associated with said vertical coordinates lying in said video frames to determine ratios and distances for all vertical coordinates lying between said vertical coordinates of said indicators in said frames; and

b) means for placing said interpolated ratios, said total real-world distance moved, and said horizontal coordinates for each said vertical coordinate in said memory locations.