Apparatus and method for three-dimensional perspective imaging of objects

• US 5,513,276 A
• Filed: 06/02/1994
• Issued: 04/30/1996
• Est. Priority Date: 06/02/1994
• Status: Expired due to Fees

• Current Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Original Assignee: The Board of Regents of the University of Colorado (University of Colorado System)
• Inventors: Theodoracatos, Vassilios E.
• Primary Examiner(s): Mancuso, Joseph
• Assistant Examiner(s): PARK, BAEIL PET
• Application Number:
  US08/253,006
• Time in Patent Office: 698 Days
• Field of Search: 348/94, 348/95, 348/135, 348/139, 348/140, 348/128, 348/43, 382/1, 382/8, 382/41, 382/106, 382/286, 382/291, 382/108, 382/154, 356/376, 356/375, 356/377
• US Class Current: 382/154
• CPC Class Codes: G01B 11/2518 Projection by scanning of the object
• CPC Class Codes: G06V 10/10 Image acquisition document image scanning and transmission H04N1/00; control of digital cameras H04N23/60
• CPC Class Codes: G06V 2201/12 Acquisition of 3D measurements of objects

Abstract

An apparatus for creating a three-dimensional perspective image of an object surface. The apparatus includes a laser, a computer system and a video camera with a sensor matrix. The laser is moved to a plurality of positions to project a light ray upon an object surface. Each projected light ray is parallel to the optical axis of the video camera. The sensor matrix of the video camera detects an image area corresponding to each one of the projected light rays. The computer system identifies an image point from each image area, calculates an image of the object surface defined by three-dimensional grid coordinates and transforms the image coordinates into three-dimensional coordinates which define the real object surface. In another embodiment, a number of lasers are arranged in an array to project parallel light rays upon the object surface. The lasers are actuated according to a predetermined sequence to project parallel light rays upon the object surface one at a time. In yet another embodiment, a plane of laser light may be directed on the object surface to produce a laser stripe on the object and an image stripe in the sensor matrix. Each point of the image stripe is correlated with a laser point and three-dimensional grid coordinate is calculated from the points of the image stripe and the corresponding laser points.

Claims

1. An apparatus for creating a three-dimensional image of an object surface, the apparatus comprising:

a light source adapted to train a projected light ray upon an object surface to produce an illuminated point on the object surface;

a video camera having an optical axis, a focal length and a vanishing point, the optical axis of the video camera being substantially parallel to the projected light ray, said video camera also having a sensor matrix defining a sensor matrix plane which is substantially perpendicular to the optical axis of the video camera, the vanishing point of the video camera being substantially at the focal length distance from the sensor matrix plane along the optical axis of the video camera toward the object;

means for determining a source point corresponding to the intersection of the sensor matrix plane and the line defined by the projected light rays wherein the vanishing point and the source point define a vanishing point line;

means for determining a sensed point lying in the sensor matrix plane and corresponding to the illuminated point on the object surface;

processing means for determining a normal line perpendicular to the sensor matrix plane and passing through the sensed point, and for computing three-dimensional image coordinates for the image point defined by the intersection of the normal line with the vanishing point line; and

transformation means for converting the three-dimensional image coordinates into three-dimensional object coordinates representing the object surface.

2. The apparatus of claim 1 wherein said processing means computes Z_B coordinates of the three-dimensional image coordinates in accordance with the formula:

##EQU17## wherein X_B and Y_B are coordinates of the image points in the plane of the sensor matrix, f is the focal length of said video camera, and X_A and Y_A are coordinates the intersection of the light rays and the plane of the sensor matrix.

3. The apparatus of claim 1 wherein said transformation means computes three-dimensional object coordinates in accordance with the matrix equation:

##EQU18## wherein X_R, Y_R and Z_B are three-dimensional real object coordinates, X_B, Y_B and Z_B are three-dimensional image coordinates, and f is the focal length of said video camera.

4. The apparatus of claim 1 further comprising:

means for calibrating said video camera.

5. The apparatus of claim 1 wherein the light source is movable in order to successively project a light ray upon different points of the object surface.

6. The apparatus of claim 1 further comprising:

a computer system having a video monitor and means for computing, storing and displaying data related to imaging the object surface.

7. The apparatus of claim 1 wherein said light source further comprises:

a laser projecting light having a wavelength of approximately 670 nanometers.

8. The apparatus of claim 1 wherein said light source further comprises:

a plurality of lasers arranged in an array to project parallel laser rays; and

means for sequentially actuating each one of said lasers.

9. The apparatus of claim 8 wherein each one of said lasers projects light having a wavelength of approximately 670 nanometers.

10. The apparatus of claim 1 further comprising:

means for computing a centroid for each one of the image areas of the sensor matrix to identify a corresponding image point within the plane of the sensor matrix.

11. A method of imaging an object surface, the steps of the method comprising:

training a projected light ray upon an object surface to produce an illuminated point on the object surface;

providing a video camera having an optical axis, a focal length, a vanishing point and a sensor matrix, the optical axis being parallel to the projected light ray, the sensor matrix defining a sensor matrix plane perpendicular to the projected light ray, the vanishing point being at the focal length distance from the sensor matrix plane along the optical axis toward the object;

determining a source point corresponding to the intersection of the sensor matrix plane and the line defined by the projected light ray, wherein the vanishing point and the source point define a vanishing point line;

viewing the object surface with the video camera to determine a sensed point lying in the sensor matrix plane and corresponding to the illuminated point on the object surface;

defining a normal line perpendicular to the sensor matrix plane and passing through the sensed point lying in the sensor matrix plane;

determining an image point corresponding to the intersection of the normal line with the vanishing point line;

computing three-dimensional image coordinates corresponding to the image point; and

transforming the three-dimensional image coordinates into three-dimensional object coordinates representing the illuminated point on the object surface.

12. The method of claim 11 further comprising the step of:

calibrating said video camera.

13. The method of claim 11 wherein the step of determining image points comprises the step of:

computing the centroid of each one of the image areas of the sensor matrix.

14. The method of claim 11 wherein the step of computing three-dimensional image coordinates comprises the step of:

computing a perspective image coordinate Z_B according to the equation;

##EQU19##

15. The method of claim 11 wherein the step of transforming three-dimensional image coordinates comprises the step of:

converting three-dimensional image coordinates into three-dimensional real object coordinates according to the matrix equation;

##EQU20##

16. A method of creating a three-dimensional image of an object surface, the steps of the method comprising:

projecting a plane of light upon an object surface to produce a stripe comprising a plurality of illuminated points on the object surface;

providing a video camera having an optical axis, a focal length, a vanishing point and a sensor matrix, the optical axis being parallel to the plane of light, the vanishing point being a focal length distance from the sensor matrix along the optical axis toward the object, the sensor matrix defining a sensor matrix plane substantially perpendicular to the plane of light;

determining a plurality of source points, each one of the source points lying on the line defined by the intersection of the sensor matrix plane with the plane defined by the projected plane of light, wherein the vanishing point and each one of the source points define a corresponding vanishing point line;

viewing the object surface with the video camera to obtain an image stripe comprising a plurality of sensed points lying in the sensor matrix plane, each one of the sensed points corresponding to one of the illuminated points on the object surface;

defining a normal line corresponding to each one of the sensed points, each normal line being perpendicular to the sensor matrix plane and passing through the corresponding one of the sensed points;

determining a plurality of image points, each one of the image points corresponding to the intersection of the vanishing point line for the corresponding one of the source points and the normal line for the corresponding one of the sensed points;

computing three-dimensional image coordinates for each one of the image points; and

transforming the three-dimensional image coordinates into three-dimensional object coordinates representing the object surface.

17. An apparatus for creating a three-dimensional image of an object surface, the apparatus comprising:

a light source adapted to train a plane of light upon an object surface to produce a stripe consisting of a plurality of illuminated points on the object surface;

a video camera having an optical axis, a focal length and a vanishing point, the optical axis of the video camera being substantially parallel to the projected plane of light, the video camera also having a sensor matrix defining a sensor matrix plane which is substantially perpendicular to the optical axis of the video camera, the vanishing point of the video camera being substantially at the focal length distance from the sensor matrix plane along the optical axis of the video camera toward the object;

means for determining a plurality of source points lying on the line defined by the intersection of the sensor matrix plane with the plane defined by the projected plane of light, wherein the vanishing point and each one of the source points define a corresponding vanishing point line;

means for determining a plurality of sensed points lying in the sensor matrix plane, each one of the sensed points corresponding to one of the illuminated points on the object surface;

processing means for determining a plurality of normal lines perpendicular to the sensor matrix plane wherein each one of the normal lines passes through a corresponding one of the sensed points, and for computing three-dimensional image coordinates for a plurality of image points wherein each one of the image points is defined by the intersection of a corresponding one of the normal lines with the vanishing point line; and

transformation means for converting the three-dimensional image coordinates into three-dimensional object coordinates representing the object surface.