Compensation for overflight velocity when stabilizing an airborne camera

• US 7,602,415 B2
• Filed: 01/15/2004
• Issued: 10/13/2009
• 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): Kelley; Christopher
• Assistant Examiner(s): Shepard; Justin E
• Application Number:
  US10/758,684
• Publication Number:
  US 20040207727A1
• Time in Patent Office: 2,098 Days
• Field of Search: 348/144, 348/169, 356/139.04, 356/139.05, 356/139.06, 244/3.16
• 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 the 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:

setting an initial line of sight for the camera that is aimed at the current position of the target;

calculating a transformation matrix C_CE for transforming from the earth reference frame to the camera reference frame;

periodically determining a static adjustment including,

calculating a position vector Δ

R^E between the aircraft and the target in the earth reference frame as;

Δ

R^E=R_target^E−

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

calculating a position vector Δ

R^C between the aircraft and the target in the camera reference frame by transforming the position vector Δ

R^E to the camera reference frame as Δ

R^C=C_CEΔ

R^E,

calculating a normalized position vector Δ

{tilde over (R)}^C as

$\mathrm{\Delta <br><br>}<br><br>{\tilde{R}}^C=\frac{\mathrm{\Delta <br><br>}<br><br><br><br>R^C}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>R^C<br><br>},$

wherein the normalized position vector indicates the difference between the actual line of sight of the camera and the line of sight needed to point to the target in the scan and tilt directions, and

setting the line of sight of the camera based at least in part on the normalized position vector Δ

{tilde over (R)}^C;

periodically determining a dynamic adjustment including,

calculating a velocity vector Δ

V^E between the aircraft and the target in the earth reference frame as;

Δ

V^E=V_target^E−

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

calculating a velocity vector Δ

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

V^E to the camera reference frame as Δ

V^C=C_CEΔ

V^E,

calculating a normalized velocity vector Δ

{tilde over (V)}^C as

$\mathrm{\Delta <br><br>}<br><br>{\tilde{V}}^C=\frac{\mathrm{\Delta <br><br>}<br><br><br><br>V^C}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>R^C<br><br>},$

wherein the normalized velocity vector indicates the angular velocity that the camera needs to move in the scan and tilt directions to compensate for overflight velocity, and

setting an angular velocity for moving the line of sight of the camera based at least in part on the normalized velocity vector Δ

{tilde over (V)}^C;

maintaining the line of sight of the camera by combining the determined dynamic and static adjustments as the attitude of the aircraft changes relative to the current position of the target, including selling an adjustment A for the camera wherein A=Δ

{tilde over (R)}^C*W+Δ

{tilde over (V)}^C and 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.

2. The method of claim 1 wherein the initial line of sight of the camera is set based on an operator centering the line of sight of the camera on the target.

3. The method of claim 1 wherein the initial line of sight of the camera is set based on the current position of the target and the current position and attitude of the vehicle.

4. The method of claim 1 wherein the vehicle is land based.

5. The method of claim 1 wherein the vehicle is airborne.

6. The method of claim 1 wherein the vehicle is space based.

7. The method of claim 1 wherein the target is at a fixed position.

8. The method of claim 1 wherein the target is moving.

9. The method of claim 1 including calculating an initial position of the target based on an initial position of the vehicle and an initial difference in altitude between the vehicle and the target.

10. The method of claim 1 including calculating the current position of the target based on the current position of the vehicle and altitude of the target.

11. The method of claim 1 including calculating the current position of the target based on the current position of the vehicle and difference in altitude between the current position of the vehicle and current position of the target.

12. The method of claim 1 wherein the attitude includes pitch, roll, and heading.

13. The method of claim 1 wherein a gyroscope is used to maintain the line of sight of the camera.

14. The method of claim 1 wherein combining the determined dynamic and static adjustments allows for smooth and continuous adjustments to be made based on velocity while correcting for accumulated errors in the line of sight.

15. A calibration system for controlling the orientation of a device to remain fixed on a target, the device being on a vehicle that is moving relative to a target, comprising:

a component that sets an initial line of sight for the camera that is aimed at the current position of the target;

a component that calculates a transformation matrix C_CE for transforming from the earth reference frame to the camera reference frame;

a component that periodically determines a static adjustment by,

calculating a position vector Δ

R^E between the vehicle and the target in the earth reference frame as;

Δ

R^E=R_target^E−

R_aircraft^E, wherein R_target^E represents the current position of the target and R_aircraft^E represents the current position of the vehicle,

calculating a position vector Δ

R^C between the vehicIe and the target in the camera reference frame by transforming the position vector Δ

R^E to the camera reference frame as Δ

R^C=C_CEΔ

R^E,

calculating a normalized position vector Δ

{tilde over (R)}^C as

$\mathrm{\Delta <br><br>}<br><br><br><br>{\tilde{R}}^C=\frac{\mathrm{\Delta <br><br>}<br><br><br><br>R^C}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>R^C<br><br>},$

 

wherein the normalized position vector indicates the difference between the actual line of sight of the camera and the line of sight needed to point to the target in the scan and tilt directions, and

setting the line of sight of the camera based at least in part on the normalized position vector Δ

{tilde over (R)}^C;

a component that periodically determines a dynamic adjustment by,

calculating a velocity vector Δ

V^E between the vehicle and the target in the earth reference frame as;

Δ

V^E=V_target^E−

V_aircraft^E, wherein V_target^E represents the current velocity of the target and V_aircraft^E represents the current velocity of the vehicle,

calculating a velocity vector Δ

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

V^E to the camera reference frame as Δ

V^C=C_CEΔ

V^E,

calculating a normalized velocity vector Δ

{tilde over (V)}^C as

$\mathrm{\Delta <br><br>}<br><br>{\tilde{V}}^C=\frac{\mathrm{\Delta <br><br>}<br><br><br><br>V^C}{<br><br>\mathrm{\Delta <br><br>}<br><br><br><br>R^C<br><br>},$

 

wherein the normalized velocity vector indicates the angular velocity that the camera needs to move in the scan and tilt directions to compensate for overflight velocity, and

setting an angular velocity for moving the line of sight of the camera based at least in part on the normalized velocity vector Δ

{tilde over (V)}^c; and

a component that maintains the line of sight of the camera by combining the determined dynamic and static adjustments as the attitude of the vehicle changes relative to the current position of the target, including setting an adjustment A for the camera wherein A=Δ

{tilde over (R)}^C*W+Δ

{tilde over (V)}^C and 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.

16. The system of claim 15 wherein the initial line of sight of the camera is set based on an operator centering the line of sight of the camera on the target.

17. The system of claim 15 wherein the initial line of sight of the camera is set based on the current position of the target and the current position and attitude of the vehicle.

18. The system of claim 15 wherein the vehicle is land based.

19. The system of claim 15 wherein the vehicle is airborne.

20. The system of claim 15 wherein the vehicle is space based.

21. The system of claim 15 wherein the target is at a fixed position.

22. The system of claim 15 wherein the target is moving.

23. The system of claim 15 including calculating an initial position of the target based on an initial position of the vehicle and an initial difference in altitude between the vehicle and the target.

24. The system of claim 15 including calculating the current position of the target based on the current position of the vehicle and altitude of the target.

25. The system of claim 15 including calculating the current position of the target based on the current position of the vehicle and difference in altitude between the current position of the vehicle and current position of the target.

26. The system of claim 15 wherein the attitude includes pitch, roll, and heading.

27. The system of claim 15 wherein a gyroscope is used to maintain the line of sight of the camera.

28. The system of claim 15 wherein combining the determined dynamic and static adjustments allows for smooth and continuous adjustments to be made based on velocity while correcting for accumulated errors in the line of sight.