Process and device for locating an object in space

• US 6,300,974 B1
• Filed: 02/13/1998
• Issued: 10/09/2001
• Est. Priority Date: 02/28/1997
• Status: Expired due to Term

• Current Assignee: Commmissariat A L'Energie Atomique
• Original Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Inventors: Letellier, Laurent, Viala, Marc
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): VO, TUNG T
• Application Number:
  US09/023,854
• Time in Patent Office: 1,334 Days
• Field of Search: H04/N.718, G06/T 1.500, 348/61, 348/62, 348/69, 348/81, 348/50, 348/82, 382/152, 382/154, 382/141, 382/20, 382/50, 382/94-95, 382/137, 382/140, 382/587, 356/142, 356/143, 356/375, 356/248, 250/589.1, 250/559.29, 345/419, 359/23
• US Class Current: 348/61
• CPC Class Codes: G01V 8/10 Detecting, e.g. by using light barriers by reflection from the object G01S17/00
• CPC Class Codes: G06T 7/73 using feature-based methods
• CPC Class Codes: G06V 10/245 by locating a pattern; Special marks for positioning

Abstract

An attempt is made to localize an object (1) with marks (3) in space, using a video camera (4). A search is made for traces of the marks (3) on the image, to deduce the directions of the marks (3) in the camera (4) view field and the position of the object (1). The algorithm used includes a step in which marks are approximately located by simple formulas, and then a step in which the estimate is improved by an error minimization calculation. Traces are modeled on the image to determine their position with high accuracy, better than the resolution pitch of the camera (4) which therefore does not need to give a very sharp image. The marks (3) are preferably passive marks and may or may not be reflecting, and do not emit any light. The system is not very sensitive to parasite lighting.

Claims

1. Process for positioning an object (1) carrying marks (3) in space, consisting of determining the positions of traces (13) of marks (3) on an image (10) taken with a camera (4), and then calculating the positions of the marks (3) with respect to the camera (4) using the positions of the traces (13) on the image (4), characterized in that it comprises a step to improve the determination of the positions of the traces (13) on the image (10) by modeling the traces (13) using predetermined geometric shape functions and calculating the positions of the shape function that best correspond to the traces, the correspondence being calculated by minimizing a difference in light intensity on the image between the trace (13) and the geometric shape function, the predetermined geometric shape function including variable parameters for taking account of deformation and dimension of aspects of the marks (3) due to distance and rotation of the object (1), the geometric shape function including a gaussian function with variable parameters for modeling the light intensity within the shape function.

6. Device for embodying the process according to claim 1, characterized in that the marks (3) have no light source and that the image taking device is a camera (4).

2. Process for positioning an object (1) carrying marks (3) in space, consisting of determining the positions of traces (13) of marks (3) on an image (10) taken with a camera (4), and then calculating the positions of the marks (3) with respect to the camera (4) using the positions of the traces (13) on the image (4), characterized in that it comprises a step to improve the determination of the positions of the traces (13) on the image (10) by modeling the traces (13) using predetermined geometric shape functions and calculating the positions of the shape function that best correspond to the traces, the correspondence being calculated by minimizing a difference in light intensity on the image between the trace (13) and the geometric shape function, the geometric shape function including a gaussian light intensity function with variable parameters, characterized in that it comprises a step in which the image (10) is reduced, using only some of the dots in the image (10), then searching for traces on the reduced image by correlating it with a reference image (11) before carrying out the step to improve the determination of the positions of traces using the complete image.

3. Process for positioning an object (1) carrying marks (3) in space, consisting of determining the positions of traces (13) of marks (3) on an image (10) taken with a camera (4), and then calculating the positions of the marks (3) with respect to the camera (4) using the positions of the traces (13) on the image (4), characterized in that it comprises a step to improve the determination of the positions of the traces (13) on the image (10) by modeling the traces (13) using predetermined geometric shape functions and calculating the positions of the shape function that best correspond to the traces, the correspondence being calculated by minimizing a difference in light intensity on the image between the trace (13) and the geometric shape function, the geometric shape function including a gaussian light intensity function with variable parameters, characterized in that it includes an extraction of portions (12) of image (10) each comprising one of the traces (13) and an adjustment of the position of image portions (12) in larger windows (14) so that they correctly surround the traces (13), maximizing correlations of image portions (12) successively adjusted in position and a reference image (11) containing a trace of a mark, before carrying out the step to improve the determination of the positions of the traces.

4. Process for positioning an object (1) carrying marks (3) in space, consisting of determining the positions of traces (13) of marks (3) on an image (10) taken with a camera (4), and then calculating the positions of the marks (3) with respect to the camera (4) using the positions of the traces (13) on the image (4), characterized in that it comprises a step to improve the determination of the positions of the traces (13) on the image (10) by modeling the traces (13) using predetermined geometric shape functions and calculating the positions of the shape function that best correspond to the traces, the correspondence being calculated by minimizing a difference in light intensity on the image between the trace (13) and the geometric shape function, the geometric shape function including a gaussian light intensity function with variable parameters, characterized in that the positions of marks (3) are calculated by an algorithm carrying out a reverse projection of traces (13) on a plane (π

) parallel to a plane of the image (10) along lines converging towards a single focal point (F), and then perpendicularly to the said parallel plane in space.

5. Process for positioning an object (1) carrying marks (3) in space, consisting of determining the positions of traces (13) of marks (3) on an image (10) taken with a camera (4), and then calculating the positions of the marks (3) with respect to the camera (4) using the positions of the traces (13) on the image (4), characterized in that it comprises a step to improve the determination of the positions of the traces (13) on the image (10) by modeling the traces (13) using predetermined geometric shape functions and calculating the positions of the shape function that best correspond to the traces, the correspondence being calculated by minimizing a difference in light intensity on the image between the trace (13) and the geometric shape function, the geometric shape function including a gaussian light intensity function with variable parameters, characterized in that the positions of marks (3) are calculated by an algorithm carrying out a reverse projection of traces (13) on a plane (π

) parallel to a plane of the image (10) along lines converging towards a single focal point (F), and then perpendicularly to the said parallel plane in space, characterized in that the marks calculated by the algorithm are projected onto the plane of the image (10) along lines converging towards the focal point (F) by calculations, to give check projections, and positions of the calculated marks are corrected to minimize an error criterion between the check projections and the traces.