Determining coordinates of a target in relation to a survey instrument having a camera

• US 8,625,086 B2
• Filed: 02/12/2008
• Issued: 01/07/2014
• Est. Priority Date: 02/12/2008
• Status: Active Grant

• Current Assignee: Trimble AB (Trimble Inc.)
• Original Assignee: Trimble AB (Trimble Inc.)
• Inventors: Vogel, Michael, Svanholm, Set, Grsser, Christian
• Primary Examiner(s): Perungavoor, Sath V
• Assistant Examiner(s): Brown, Jr., Howard D
• Application Number:
  US12/735,582
• Publication Number:
  US 20110007154A1
• Time in Patent Office: 2,156 Days
• Field of Search: 348/142
• US Class Current: 356/141.5
• CPC Class Codes: G01C 1/04 combined with cameras
• CPC Class Codes: G01C 11/06 by comparison of two or more pictures of the same area
• CPC Class Codes: G01C 15/00 Surveying instruments or accessories not provided for in groups G01C1/00 - G01C13/00

Abstract

A method is disclosed for determining coordinates of a target in relation to a surveying instrument wherein a first image is captured using a camera in a first camera position and orientation, a target is selected by identifying an object point in the first image, and first image coordinates of the object point in the first image are measured. The surveying instrument is then rotated around the rotation center so that the camera is moved from the first camera position and orientation to a second camera position and orientation, while retaining the rotation center of the surveying instrument in a fixed position. A second image is captured using the camera in the second camera position and orientation, the object point identified in the first image is identified in the second image, and second image coordinates of the object point in the second image are measured. Target coordinates in relation to the rotation center of the surveying instrument are then determined based on the first camera position and orientation, the first image coordinates, the second camera position and orientation, the second image coordinates, and camera calibration data. Furthermore, a surveying instrument for performing the method is disclosed.

Claims

1. A method for determining coordinates of a target in relation to a surveying instrument comprising a camera, comprising:

capturing a first image using the camera in a first camera position and orientation, said first camera position being eccentric to a rotation center of the surveying instrument;

selecting a target by identifying an object point in the first image;

measuring first image coordinates of the object point in the first image;

rotating the surveying instrument around the rotation center so that the camera is moved from the first camera position and orientation to a second camera position and orientation, while retaining the rotation center of the surveying instrument in a fixed position, said second camera position being eccentric to the rotation center of the surveying instrument;

capturing a second image using the camera in the second camera position and orientation;

identifying, in the second image, the object point identified in the first image, wherein the identifying includes,

selecting a minimum distance and a maximum distance from the first camera position along an imaging ray of the target in the first image, between which minimum distance and maximum distance the target is located,

determining a section of an epipolar line in the second image on which the object point is located based on the maximum distance, the minimum distance, the first camera position and orientation, the second camera position and orientation, the first image coordinates, and camera calibration data, and

identifying, along the section of the epipolar line in the second image, the object point identified in the first image;

measuring second image coordinates of the object point in the second image; and

determining target coordinates of the target in relation to the rotation center of the surveying instrument based on the first camera position and orientation, the first image coordinates, the second camera position and orientation, the second image coordinates, and camera calibration data.

2. The method of claim 1, wherein the minimum distance is selected as the minimum distance of the surveying instrument.

3. The method of claim 1, wherein if the identified object point is not closer than a threshold distance from a closest corner of the first image the following steps are performed:

determining, based on the position of the object point in the first image, a revised rotation of the surveying instrument around the rotation center resulting in the object point being closer than a threshold distance from a closest corner of an image captured with the camera after the revised rotation;

rotating the surveying instrument around the rotation center by the revised rotation so that the camera is moved from the first camera position and orientation to a revised first camera position and orientation;

capturing a revised first image using the camera in the revised first position and orientation;

identifying, in the revised first image, the object point identified in the first image;

revising the first image coordinates to measured image coordinates of the object point in the revised first image.

4. The method of claim 3, wherein identifying, in the revised first image, the object point identified in the first image comprises:

determining an epipolar line in the revised first image on which the object point is located, based on the first camera position and orientation, the revised camera position and orientation, the first image coordinates and camera calibration data; and

identifying, along the epipolar line in the revised first image, the object point identified in the first image.

5. The method of claim 4, wherein identifying, in the revised first image, the object point identified in the first image comprises:

selecting a minimum distance and a maximum distance from the first camera position along the imaging ray of the target in the first image, between which minimum distance and maximum distance the target is located,

determining, based on the maximum distance, and the minimum distance, a section of the epipolar line in the revised first image on which the object point is located; and

identifying, along the section of the epipolar line in the revised first image, the object point identified in the first image.

6. The method of claim 1, wherein the object point is identified in the first image by operator selection.

7. The method of claim 1, wherein the object point is identified in the first image by automatic image analysis.

8. The method of claim 1, wherein the object point identified in the first image is identified in the second image by automatic image analysis.

9. The method of claim 1, wherein the object point identified in the first image is identified in the second image by user selection.

10. The method of claim 1, further comprising:

determining a direction from the rotation center of the surveying instrument towards the target based on the determined coordinates of the target.

11. The method of claim 10, further comprising:

rotating the surveying instrument so that a line of sight of the surveying instrument is directed in the direction towards the target.

12. The method of claim 11, further comprising:

measuring a distance to the target using distance measuring capabilities within the surveying instrument.

13. The method of claim 1, further comprising:

determining a distance from the rotation center of the surveying instrument to the target based on the determined target coordinates.

14. The method of claim 1, wherein said rotation of the surveying instrument around the rotation center so that the camera is moved from the first camera position and orientation to a second camera position and orientation comprises:

rotating the surveying instrument 180 degrees around a first of the two rotational axes of the rotation center; and

rotating the surveying instrument 180 degrees around a second of the two rotational axes of the rotation center.

15. A computer program product stored on a non-transitory computer-readable medium, the computer program product comprising computer program code portions configured to perform the method of claim 1 when loaded and executed in a computer.

16. A surveying instrument, comprising:

a camera configured to capture images from a first camera position and orientation and a second camera position and orientation different from the first camera position and orientation, the first and second camera positions and orientations being eccentric to a rotation center of the surveying instrument, while retaining the rotation center of the surveying instrument in a fixed position;

a display configured to display images captured by said camera from the different positions and orientations;

an identifying mechanism configured to identify an object point corresponding to a selected target in the displayed images, said identifying mechanism being configured to,

select a minimum distance and a maximum distance from the first camera position along an imaging ray of the target in the first image, between which minimum distance and maximum distance the target is located,

determine a section of an epipolar line in the second image on which the object point is located based on the maximum distance, the minimum distance, the first camera position and orientation, the second camera position and orientation, the first image coordinates, and camera calibration data, and

identify, along the section of the epipolar line in the second image, the object point identified in the first image;

a measuring mechanism configured to measure image coordinates of the object point in the displayed images;

a rotating mechanism configured to rotate the surveying instrument around the rotation center of the surveying instrument; and

a determining mechanism configured to determine coordinates of the target in relation to the rotation center of the surveying instrument, based on the first camera position and orientation, the first image coordinates, the second camera position and orientation, the second image coordinates, and camera calibration data.

17. The instrument of claim 16, wherein the identifying mechanism is implemented as a cursor movable across the displayed images.

18. The instrument of claim 16, wherein the identifying mechanism is implemented using a touch display, where the object point can be identified by clicking or tapping on the display.

19. The instrument of claim 16, wherein the identifying mechanism is implemented using image processing software.