Method and system for the determination of object positions in a volume

• US 20090324009A1
• Filed: 06/27/2008
• Published: 12/31/2009
• Est. Priority Date: 06/27/2008
• Status: Active Grant

• Current Assignee: Waldean A. Schulz
• Original Assignee: Waldean A. Schulz
• Inventors: Schulz, Waldean A.
• Granted Patent: US 8,086,026 B2
• Time in Patent Office: Days
• US Class Current: 382/103
• CPC Class Codes: G06T 2207/10021 Stereoscopic video; Stereoscopic image sequence
• CPC Class Codes: G06T 2207/30204 Marker
• CPC Class Codes: G06T 7/13 Edge detection
• CPC Class Codes: G06T 7/73 using feature-based methods

Abstract

A method or a system embodiment determines positional information about a moveable object to which is affixed a pattern of stripes having reference lines. A method determines image lines of stripe images of each stripe within at least two video frames, uses the image lines to prescribe planes having lines of intersection, and determines a transformation mapping reference lines to lines of intersection. Position information about the object may be derived from the transformation. A system embodiment comprises a pattern of stripes in a known fixed relationship to an object, reference lines characterizing the stripes, two or more cameras at known locations, a digital computer adapted to receive video frames from the pixel arrays of the cameras, and a program stored in the computer'"'"'s memory. The program performs some or all of the method. When there are two or more moveable objects, an embodiment may further determine the position information about a first object to be transformed to a local coordinate system fixed with respect to a second object.

Claims

1. A system for determining position information about a first object in a volume, comprising:

a global coordinate system defined in the volume;

a local coordinate system in a known fixed relationship to the first object;

a pattern of two or more stripes in a fixed relationship to the first object, wherein a first stripe of the pattern is characterized by a first reference line defined relative to the local coordinate system, and a second stripe of the pattern is characterized by a second reference line defined relative to the local coordinate system;

two or more cameras, wherein each camera can output a 2-dimensional video frame, and wherein each video frame has a known relationship to the global coordinate system;

a digital computer adapted to receive the video frame output from each camera; and

a memory connected to the computer and containing a program of instructions which cause the computer to;

locate a first set of stripe images of the first stripe, wherein each image in the first set of stripe images is in the video frame output by a camera of the two or more cameras,

locate a second set of stripe images of the second stripe, wherein each image in the second set of stripe images is in the video frame output by a camera of the two or more cameras,

determine, for each image of the first set of stripe images, a first image line in the video frame containing the image, wherein the first image line prescribes a first plane in the volume;

determine, for each image of the second set of stripe images, a second image line in the video frame containing the image, wherein the second image line prescribes a second plane in the volume;

compute a first line of intersection of the first planes prescribed by at least two of the first image lines,

compute a second line of intersection of the second planes prescribed by at least two of the second image lines,

determine a transformation between the local coordinate system and the global coordinate system, wherein the transformation maps the first reference line to the first line of intersection, and wherein the transformation maps the second reference line to the second line of intersection, and

determine from the transformation the position information about the first object.

2. The system of claim 1, wherein at least one stripe of the two or more stripes has straight edges.

3. The system of claim 1, wherein at least one stripe of the two or more stripes has a straight centerline.

4. The system of claim 1, wherein the reference line characterizes an edge of the stripe.

5. The system of claim 1, wherein the reference line characterizes a centerline of the stripe.

6. The system of claim 1, wherein at least one stripe of the pattern has at least one feature which distinguishes the pattern from another pattern.

7. The system of claim 6, wherein the at least one feature is at least one of color, relative position, relative length, and relative width.

8. The system of claim 1, wherein at least one stripe of the pattern has at least one feature which differentiates the one stripe from another stripe of the pattern.

9. The system of claim 8, wherein the at least one feature is at least one of color, relative position, relative length, and relative width.

10. The system of claim 1, wherein the position information about the first object includes the time at which the position information was computed.

11. The system of claim 1, wherein the position information about the first object includes a location of the first object.

12. The system of claim 11, wherein a reference point defined as coordinates relative to the local coordinate system is mapped by the transformation to coordinates in the global coordinate system, and wherein the position information includes the coordinates of the reference point relative to the global coordinate system.

13. The system of claim 1, wherein the position information about the first object includes an orientation of the first object.

14. The system of claim 13, wherein at least one reference vector defined as coordinates relative to the local coordinate system is mapped by the transformation to coordinates in the global coordinate system, and wherein the position information includes the coordinates of the reference vector relative to the global coordinate system.

15. The system of claim 1, wherein the position information of the first object is determined in relation to a second coordinate system fixed with respect to a second pattern of lines affixed to a second object by which the system determines position information of the second object.

16. A method for determining positional information about a first object in a volume, comprising:

defining a global coordinate system in the volume;

defining a local coordinate system in a known fixed relationship to the first object;

affixing a first pattern of two or more stripes in a relationship to the first object;

characterizing a first stripe of the first pattern by a first reference line defined relative to the local coordinate system;

characterizing a second stripe of the first pattern by a second reference line defined relative to the local coordinate system;

positioning two or more cameras to view at least a portion of the volume;

outputting a video frame from each of the two or more cameras, wherein each video frame has a known relationship to the volume;

locating a first set of images of the first stripe, wherein each image in the first set of images is contained in the video frame output by a camera of the two or more cameras,

locating a second set of images of the second stripe, wherein each image in the second set of images is contained in the video frame output by a camera of the two or more cameras,

for each image in the first set of images, determining a first image line in the video frame containing the image, wherein the first image line prescribes a first plane in the volume;

for each image in the second set of images, determining a second image line in the video frame containing the image, wherein the second image line prescribes a second plane in the volume;

computing a first line of intersection of the first planes prescribed by at least two of the first image lines;

computing a second line of intersection of the second planes prescribed by at least two of the second image lines;

determining a transformation between the local coordinate system and the global coordinate system, wherein the transformation maps the first reference line to the first line of intersection, and wherein the transformation maps the second reference line to the second line of intersection; and

determining the position information about the first object from the transformation.

17. The method of claim 16, wherein the first reference line characterizes an edge of the first stripe, and the second reference line characterizes an edge of the second stripe.

18. The method of claim 16, wherein the first reference line characterizes a centerline of the first stripe, and the second reference line characterizes a centerline of the second stripe.

19. The method of claim 16, additionally comprising:

distinguishing the first pattern of stripes from any other pattern of stripes using at least one feature of at least one stripe of the first pattern.

20. The method of claim 19, wherein the at least one feature is at least one of color, relative position, relative length, and relative width.

21. The method of claim 16, additionally comprising:

differentiating the first stripe of the first pattern from the second stripe of the first pattern using at least one feature which differs between the first stripe and the second stripe.

22. The method of claim 21, wherein the at least one feature is at least one of color, relative position, relative length, and relative width.

23. The method of claim 16, wherein the determining of the position information includes determining the time at which one camera of the two or more cameras output the video frame of one camera used to determine the position information.

24. The method of claim 16, wherein the determining of the position information includes determining a location of the first object.

25. The method of claim 24, wherein the determining a location of the first object includes using the transformation to map a reference point defined as coordinates relative to the local coordinate system of the first object to coordinates relative to the global coordinate system.

26. The method of claim 16, wherein the determining of the position information includes determining an orientation of the first object.

27. The method of claim 26, wherein the determining an orientation of the first object includes using the transformation to map at least one reference vector defined as coordinates relative to the local coordinate system of the first object to coordinates relative to the global coordinate system.

28. The method of claim 16, additionally comprising:

determining second position information about a second object on which is defined a second coordinate system; and

determining the position information about the first object with respect to the second coordinate system.