Compensation for overflight velocity when stabilizing an airborne camera

• US 8,405,723 B2
• Filed: 10/06/2009
• Issued: 03/26/2013
• Est. Priority Date: 01/17/2003
• Status: Active Grant

• Current Assignee: Insitu Incorporated (The Boeing Co.)
• Original Assignee: Insitu Incorporated (The Boeing Co.)
• Inventors: von Flotow, Andreas H., Mercadal, Mathieu
• Primary Examiner(s): SHEPARD, JUSTIN E
• Application Number:
  US12/574,606
• Publication Number:
  US 20100110187A1
• Time in Patent Office: 1,267 Days
• Field of Search: 348/144
• US Class Current: 348/144
• CPC Class Codes: G01C 11/025 by scanning the object
• CPC Class Codes: G06T 2207/10016 Video; Image sequence
• CPC Class Codes: G06T 2207/10032 Satellite or aerial image; Remote sensing
• CPC Class Codes: G06T 2207/30181 Earth observation
• CPC Class Codes: G06T 2207/30212 Military
• CPC Class Codes: G06T 2207/30236 Traffic on road, railway or crossing
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51

Abstract

A method and system for maintaining the line of sight of an airborne camera fixed on a target by compensating for overflight velocity of the aircraft. The compensation system automatically commands an angular velocity of the line of sight to maintain the camera pointing at the target being overflown. This angular velocity of the line of sight is computed based upon the aircraft overflight velocity and upon a vector from the aircraft to the target. This automatic compensation for aircraft overflight velocity causes the line of sight to remain fixed upon the target. The compensation system drives a gimbal system upon which the camera is mounted to perform this compensation automatically.

Claims

1. A method for controlling a line of sight of a camera to remain fixed on a target, the camera being on an aircraft whose current position is moving at a velocity relative to a current position of the target, the method comprising:

determining a static adjustment including,

calculating a first position vector between the aircraft and the target, and

calculating a normalized position vector indicating the difference in scan and tilt directions between a current line of sight of the camera and a desired line of sight to the target as indicated by the calculated position vector at least in part by dividing coordinates of the first position vector by a distance from the aircraft to the target;

determining a dynamic adjustment including,

calculating a first velocity vector between the aircraft and the target, and

calculating a normalized velocity vector indicating an angular velocity that the camera is to move in the scan and tilt directions to compensate for overflight velocity as indicated by the calculated velocity at least in part by dividing coordinates of the first velocity vector by the distance from the aircraft to the target; and

maintaining the line of sight of the camera based at least in part on a weighted sum of the determined static and dynamic adjustments.

2. The method of claim 1, wherein the first position vector, Δ

R, is calculated as Δ

R=R_target−

R_aircraft, wherein R_target represents the current position of the target and R_aircraft represents the current position of the aircraft.

3. The method of claim 1 wherein the first velocity vector, Δ

V, is calculated as Δ

V=V_target−

V_aircraft, wherein V_target represents the current velocity of the target and V_aircraft represents the current velocity of the aircraft.

4. A method for controlling a line of sight of a camera to remain fixed on a target, the camera being on an aircraft whose current position is moving at a velocity relative to a current position of the target, the method comprising:

determining a static adjustment including,

calculating a first position vector between the aircraft and the target, wherein the first position vector, Δ

R, is calculated as Δ

R=R_target−

R_aircraft, wherein R_target represents the current position of the target and R_aircraft represents the current position of the aircraft, and

calculating a normalized position vector indicating the difference in scan and tilt directions between a current line of sight of the camera and a desired line of sight to the target as indicated by the calculated position vector;

determining a dynamic adjustment including,

calculating a first velocity vector between the aircraft and the target, and

calculating a normalized velocity vector indicating an angular velocity that the camera is to move in the scan and tilt directions to compensate for overflight velocity as indicated by the calculated velocity;

maintaining the line of sight of the camera based at least in part on a weighted sum of the determined static and dynamic adjustments; and

calculating a second position vector between the camera and the target in a camera reference frame, Δ

R^C, by transforming the first position vector to the camera reference frame.

5. The method of claim 4 wherein the normalized position vector, Δ

{tilde over (R)}^C, is calculated as

6. A method for controlling a line of sight of a camera to remain fixed on a target, the camera being on an aircraft whose current position is moving at a velocity relative to a current position of the target, the method comprising:

determining a static adjustment including,

calculating a first position vector between the aircraft and the target, and

calculating a normalized position vector indicating the difference in scan and tilt directions between a current line of sight of the camera and a desired line of sight to the target as indicated by the calculated position vector;

determining a dynamic adjustment including,

calculating a first velocity vector between the aircraft and the target, wherein the first velocity vector, Δ

V, is calculated as Δ

V=V_target−

V_aircraft, wherein V_target represents the current velocity of the target and V_aircraft represents the current velocity of the aircraft, and

calculating a normalized velocity vector indicating an angular velocity that the camera is to move in the scan and tilt directions to compensate for overflight velocity as indicated by the calculated velocity;

maintaining the line of sight of the camera based at least in part on a weighted sum of the determined static and dynamic adjustments; and

transforming the first velocity vector to a second velocity vector between the aircraft and the target in a camera reference frame Δ

V^C.

7. The method of claim 6 wherein the normalized velocity vector, Δ

V^C, is calculated as

8. A method for controlling a line of sight of a camera to remain fixed on a target, the camera being on an aircraft whose current position is moving at a velocity relative to a current position of the target, the method comprising:

determining a static adjustment including,

calculating a first position vector between the aircraft and the target, and

calculating a normalized position vector indicating the difference in scan and tilt directions between a current line of sight of the camera and a desired line of sight to the target as indicated by the calculated position vector;

determining a dynamic adjustment including,

calculating a first velocity vector between the aircraft and the target, and

calculating a normalized velocity vector indicating an angular velocity that the camera is to move in the scan and tilt directions to compensate for overflight velocity as indicated by the calculated velocity; and

maintaining the line of sight of the camera based at least in part on a weighted sum of the determined static and dynamic adjustments, wherein maintaining the line of sight of the camera includes setting an adjustment A calculated as A=P*W+V, wherein P represents the calculated normalized position vector, V represents the calculated normalized velocity vector, and W represents a weighting factor based at least in part on the accuracy of the measurements used to calculate the static and dynamic adjustments.

9. A method for controlling a line of sight of a camera, the method comprising:

determining a static adjustment including,

calculating a position vector between the camera and the target Δ

R as Δ

R=R_target−

R_camera, wherein R_target represents the current position of the target and R_camera represents the current position of the camera,

calculating a position vector between the camera and the target in a camera reference frame Δ

R^C by transforming the position vector Δ

R to the camera reference frame,

calculating a normalized position vector Δ

{tilde over (R)}^C as

10. The method of claim 9 wherein the camera is mounted to an aircraft.

11. The method of claim 9, further comprising:

determining a dynamic adjustment based at least in part on a velocity between the camera and the target.

12. The method of claim 11 wherein determining a dynamic adjustment further includes:

calculating a normalized velocity vector Δ

{tilde over (V)}^C indicating an angular velocity that the camera is to move in the scan and tilt directions to compensate at least in part for the velocity between the camera and the target.

13. The method of claim 12, further comprising:

maintaining the line of sight of the camera based at least in part on an adjustment A calculated as A=Δ

{tilde over (R)}^C*W+Δ

{tilde over (V)}^C, wherein W represents a weighting factor based on the accuracy of the measurements used to calculate the dynamic and static adjustments.

14. The method of claim 11 wherein determining a static adjustment and determining a dynamic adjustment are performed serially.

15. A system for controlling a line of sight of a camera comprising:

a component that determines a dynamic adjustment at least in part by,

calculating a velocity vector Δ

V^E between the camera and the target in an earth reference frame as Δ

V^E=V_target^E−

V_camera^E, wherein V_target^E represents the current velocity of the target and V_camera^E represents the current velocity of the camera,

calculating a velocity vector Δ

V^C between the camera and the target in a camera reference frame by transforming the velocity vector Δ

V^E to the camera reference frame, and

calculating a normalized velocity vector Δ

V^C as

16. The system of claim 15, further comprising:

a component that determines a static adjustment based at least in part on a difference in position between the camera and the target.

17. The system of claim 16, wherein determining a static adjustment further includes:

calculating a normalized position vector Δ

{tilde over (R)}^C indicating the difference in scan and tilt directions between a current line of sight of the camera and a line of sight to the target.

18. The system of claim 17, further comprising:

a component that maintains the line of sight of the camera based on an adjustment A calculated as A=Δ

{tilde over (R)}^C*W+Δ

{tilde over (V)}^C, wherein W represents a weighting factor based at least in part on the accuracy of the measurements used to calculate the dynamic and static adjustments.

19. The system of claim 16 wherein the component that determines a dynamic adjustment and the component that determines a static adjustment are invoked in serial.

20. The system of claim 15 wherein the velocity vector Δ

V^C is calculated as Δ

V^C=C_CEΔ

V^E, wherein C_CE represents a transformation matrix for transforming from the earth reference frame to the camera reference frame.

21. A method for controlling a line of sight of an airborne camera to remain fixed on a target, the camera moving at a velocity relative to the target, the method comprising:

determining a static adjustment command indicating differences in scan and tilt directions between a current line of sight of the camera and a desired line of sight to the target;

determining a dynamic adjustment command indicating an angular velocity at which the camera is to move in the scan and tilt directions to compensate for overflight velocity;

combining the adjustment commands with a weighting function to determine a control command, wherein a weight applied to the static adjustment is different from a weight applied to the dynamic adjustment; and

applying the control command to the camera.

22. The method of claim 21 wherein a difference between a scan coordinate adjustment between the current line of sight of the camera and the desired line of sight to the target and a velocity at which the camera should be scanning to keep the target in its line of sight and a scan rate of the camera provided by a gyro controls a velocity of gimbal motors.

23. The method of claim 21 wherein a difference between a tilt coordinate adjustment between the current line of sight of the camera and the desired line of sight to the target and a velocity at which the camera should be tilting to keep the target in its line of sight and a tilt rate of the camera provided by a gyro controls a velocity of gimbal motors.

24. A camera sighting adjustment method for a gimbaled camera having capability for scan and tilt adjustments, comprising the steps of:

combining a static adjustment command indicating scan and tilt direction adjustments with a dynamic adjustment command indicating an angular velocity at which the camera is to move in the scan and tilt directions to compensate for overflight velocity using a weighting function to determine a control command, wherein a weight applied to the static adjustment is different from a weight applied to the dynamic adjustment;

applying the control command to the camera;

determining a first line of sight to a target at a first time;

determining a second line of sight to the target at a second time after the first time;

converting the first line of sight to the target to an earth reference frame;

converting the second line of sight to the target to the earth reference frame; and

determining an altitude of the target based at least in part on a point of intersection of the converted first line of sight to the target and the converted second line of sight to the target.

25. A camera sighting adjustment method for a gimbaled camera having capability for scan and tilt adjustments, comprising the steps of:

combining a static adjustment command indicating scan and tilt direction adjustments with a dynamic adjustment command indicating an angular velocity at which the camera is to move in the scan and tilt directions to compensate for overflight velocity using a weighting function to determine a control command, wherein a weight applied to the static adjustment is different from a weight applied to the dynamic adjustment;

applying the control command to the camera; and

calculating a velocity of a target based at least in part on a series of centering of images on the target or a series of received indications of where the target is within the images to compensate for overflight velocity.