Method for calibrating the initial position and the orientation of one or several mobile cameras

• US 6,594,600 B1
• Filed: 07/13/1999
• Issued: 07/15/2003
• Est. Priority Date: 10/24/1997
• Status: Expired due to Fees

• Current Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Original Assignee: Commissariat a L'Energie Atomique (AES Corporation)
• Inventors: Letellier, Laurent, Guerin, Jean-Pierre, Arnoul, Patrick, Viala, marc
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): Barbee, Manuel L.
• Application Number:
  US09/331,112
• Time in Patent Office: 1,463 Days
• Field of Search: 702/85, 702/91, 702/92, 702/94, 702/95, 702/127, 702/150-153, 702/97, 702/158, 702/159, 702/183, 332/031.8, 332/86, 332/88, 382/151, 382/154, 348/135, 348/137, 348/141, 348/148
• US Class Current: 702/94
• CPC Class Codes: G01B 11/2755 using photoelectric detection means
• CPC Class Codes: G01B 2210/12 Method or fixture for calibrating the wheel aligner
• CPC Class Codes: G01B 2210/143 One or more cameras on each side of a vehicle in the main embodiment
• CPC Class Codes: G01B 2210/30 Reference markings, reflector, scale or other passive device
• CPC Class Codes: G01B 2210/303 fixed to the ground or to the measuring station
• CPC Class Codes: G01C 11/06 by comparison of two or more pictures of the same area
• CPC Class Codes: G06T 7/80 Analysis of captured images to determine intrinsic or extrinsic camera parameters, i.e. camera calibration
• CPC Class Codes: G06T 7/85 Stereo camera calibration

Abstract

A method of calibrating a camera (4, 22) disposed on a mobile support (21). The camera takes an image of a test object formed of at least three marks appearing in the field of the camera, and analysis of the image gives the initial position and orientation of the camera with respect to that of the test object, which are known in an application. The support (21) can then be moved towards an object (28) of which the camera takes images. As the movements of the support are measured accurately, analysis of the images of the object gives the precise position and orientation of the object with respect to the camera and with respect to the test object. One application is the recording of road signs (28) in order to compose databases for network management or for an on-board navigation system.

Claims

1. A method of calibrating the original position and orientation of a camera disposed on a mobile support in an environment, comprising:

providing the environment with a test object at a known position and orientation;

taking an image of the test object with the camera;

analyzing the image of the test object with a processing system by reading positions of tracks (Pp) of characteristic marks of the test object on the image and deducing directions and distances between the characteristic marks and the camera, and then a position and an orientation of the camera with respect to the test object; and

deducing the directions and distances between the characteristic marks and the calibration camera by carrying out a retro-projection of the centers of the tracks of the characteristic marks of the test object first on to a plane (II) passing through the origin of the test object reference frame and parallel to the plane of the image along lines converging towards a single focus (F), then in space, perpendicular to the said parallel plane in order to obtain retro-projection points (°

P) on to the plane of the image along lines converging towards the focus (F) in order to obtain projection points (°

Pp) , and a positional correction of the retro-projection points in order to minimize an error estimation criterion between coordinates of the centers of the tracks (Pp) of the characteristic marks and the projection points (°

pp).

2. A method for calibrating the original position and orientation of a first camera disposed on a mobile support in an environment with respect to a second camera, the cameras being disposed on independent supports mobile in the environment, the method comprising:

providing the first camera with a calibration camera and the second camera with a test object at a known position and orientation;

taking an image of the test object with the calibration camera;

analyzing the image of the test object with a processing system by reading position of tracks (Pp) of characteristic marks of the test object on the image;

deducing directions and distances between the characteristic marks and the calibration camera, then a position and an orientation of the calibration camera with respect to the test object, and then of the first camera with respect to the second camera, wherein the directions and distances between the characteristic marks and the calibration camera are deduced by carrying out a retro-projection of the centers of the tracks of the characteristic marks of the test object first on to a plane (II) passing through the origin of the test object reference frame and parallel to the plane of the image along lines converging towards a single focus (F), then in space, perpendicular to the said parallel plane in order to obtain retro-projection points (°

P), and then, iteratively, a projection of the retro-projection points (°

P) on to the plane of the image along lines converging towards the focus (F) in order to obtain projection points (°

Pp) , and a positional correction of the retro-projection points in order to minimize an error estimation criterion between coordinates of the centers of the tracks (Pp) of the characteristic marks and die projection points (°

Pp).

3. A method for calibrating the original position and orientation of a first camera disposed on a mobile support in an environment with respect to a second camera, the cameras being disposed on independent supports mobile in the environment, the method comprising:

providing the first camera with a calibration camera and the second camera with a test object at a known position and orientation;

taking an image of the test object with the calibration camera;

analyzing the image of the test object with a processing system by reading position of tracks (Pp) of characteristic marks of the test object on the image;

deducing directions and distances between the characteristic marks and the calibration camera, then a position and an orientation of the calibration camera with respect to the test object, and then of the first camera with respect to the second camera, wherein the test object comprises at least three marks in the field of the camera to be calibrated,

wherein the directions and distances between the characteristics marks and the calibration camera are deduced by carrying out a retro-projection of the centers of the tracks of the characteristic marks of the test object first on to a plane (II) passing through the origin of the test object reference frame and parallel to the plane of the image along lines converging towards a single focus (F), then in space, perpendicular to the said parallel plane in order to obtain retro-projection points (°

P), and then, iteratively, a projection of the retro-projection points (°

P) on to the plane of the image along lines converging towards the focus (F) in order to obtain projection points (°

Pp) , and a positional correction of the retro-projection points in order to minimize an error estimation criterion between coordinates of the centers of the tracks (Pp) of the characteristic marks and The projection points (°

Pp).

4. A method for calibrating the original position and orientation of a first camera disposed on a mobile support in an environment with respect to a second camera, the cameras being disposed on independent supports mobile in the environment, the method comprising:

providing the first camera with a calibration camera and the second camera with a test object at a known position and orientation;

taking an image of the test object with the calibration camera;

analyzing the image of the test object with a processing system by reading position of tracks (Pp) of characteristic marks of the test object on the image;

deducing directions and distances between the characteristic marks and the calibration camera, then a position and an orientation of the calibration camera with respect to the test object, and then of the first camera with respect to the second camera,

wherein the position and the orientation of the calibration camera with respect to the test object are deduced in the form of a position (t) and an orientation (R) of the camera to be calibrated with respect to a reference frame related to the test object,

wherein the directions and distances between the characteristic marks and the calibration camera are deduced by carrying out a retro-projection of the centers of the tracks of the characteristic marks of the test object first on to a plane (II) passing through the original of the test object reference frame and parallel to the plane of the image along lines converging towards a single focus (F), then in space, perpendicular to the said parallel plane in order to obtain retro-projection points (°

P), and then, iteratively, a projection of the retro-projection points (°

P) on to the plane of the image along lines converging towards the focus (F) in order to obtain projection points (°

Pp) , and a positional correction of the retro-projection points in order to minimize an error estimation criterion between coordinates of the centers of the tracks (Pp) of the characteristic marks and the projection points (°

Pp).