METHOD OF PERSPECTIVE TRANSFORMATION IN SCANNED RASTER VISUAL DISPLAY

• US 3,725,563 A
• Filed: 12/23/1971
• Issued: 04/03/1973
• Est. Priority Date: 12/23/1971
• Status: Expired due to Term

• Current Assignee: Cae-Link Corporation
• Original Assignee: Brian J. Woycechowsky
• Inventors: Woycechowsky, Brian J.
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Dilidine, Jr., R. Stephen
• Application Number:
  US05/211,372
• Time in Patent Office: 467 Days
• Field of Search: 178/DIG.20,DIG.35 35/10.2,12N 235/186 343/7.9
• US Class Current: 434/43
• CPC Class Codes: G09B 9/302 the image being transformed by computer processing, e.g. updating the image to correspond to the changing point of view

Abstract

A general method of providing perspective transformations in a visual display system having an image generated by a scanned raster device such as a CRT or television projector is shown. The television display is a window out of which an observer views a simulated picture of terrain. The line of sight from the observer passing through the instantaneous spot position on the window is used to find a ground intersection point, the location of this point on an image source, such as film, is found and a video signal representing that image is generated by positioning the scan of an image pick up device to that point on the image source.

Claims

1. In a display system for presenting to an observer a desired simulated scene of the earth'"'"''"'"'s surface as viewed from the observer'"'"''"'"'s viewpoint, comprising an image source depicting a portion of the earth'"'"''"'"'s surface as viewed from an image viewing point, at least part of which scene contains the same information as that contained in the desired scene;

a device with a controllable first spot for scanning the image source to develop a video signal, a display located within the observer'"'"''"'"'s field of view to form a simulated window through which the observer may view said simulated scene, said display being of the type forMed by scanning a second spot across the display to form a raster and modulating said second spot with the video signal developed by said device, a method of driving said first spot to obtain an image of the desired scene in proper perspective on said display comprising;

a. determining the simulated point of intersection with the earth'"'"''"'"'s surface of a line from the observer passing through the instantaneous position of the second scanning spot on the display window;

b. determining the location on the image source of the depicting thereon of said earth intersection point; and

c. positioning the first spot so that the video signal developed corresponds to said location on said image source.

2. The invention according to claim 1 wherein said image source is optically rotated to simulate rotation of said display window and further including the step of compensating for said rotation whereby the scanning first spot will generally follow a path more nearly approximating a normal raster.

3. The invention according to claim 1 wherein the steps of determining said earth intersection point and said location on said image source comprise:

a. determining a first set of direction cosines of the trainer body axes to a horizontal referenced axis system;

b. using said direction cosines to compute the components of said observers'"'"''"'"' eye position with respect to the simulated center of gravity in said horizontal reference axis system;

c. determining a second set of direction cosines of the display window axes to said body axes;

d. determining from the scan waveforms of said second spot the direction of a line from the observer to the instantaneous position of said second spot in the window axes frame;

e. using said second set of direction cosines to determine the direction of a line from the origin of said window axes passing through said second spot with respect to said body axes;

f. using said first set of direction cosines to reference the direction of said line to the horizontal reference axes;

g. determining the location of said observers'"'"''"'"' eyepoint with respect to said image viewing point;

h. determining from said line referenced to said horizontal axes and the altitude and location of said observers'"'"''"'"' eyepoint with respect to said image viewing point the intersection point with the earth'"'"''"'"'s surface referenced to said image viewing point with respect to the horizontal axes system;

i. determining the direction of a line from said image of viewing point to said intersection point with respect to an axes system referenced to the image source;

j. using the direction of said line reference to said image source axes to determine the location on said image source of the depiction of said earth intersection point.

4. The invention according to claim 3 wherein said display is a wide angle spherical display having a fixed frame of reference, only a relatively small portion of which is modulated by said video signal, the center of said portion is movable and may be defined by a latitude and longitude, said second set of direction cosines are the fixed display frame to body axes direction cosines;

and the direction of said line in said display frame is obtained by adding the scan wave forms of said second spot to said latitude and longitude.

5. The invention according to claim 3 wherein the steps of determining said first set of direction cosines, using said first set of direction cosines to compute said observer'"'"''"'"'s eye position, determining said second set of direction cosines, and determining the location of said observer'"'"''"'"'s eyepoint with respect to said image viewing point are performed in a digital computer and the remaining steps performed by analog computing means.

6. The invention according to claim 5 wherein the results of the digital computation are combined into a third set of direction cosines so that the steps of determining the direction of a line through said second spot, referencing said spot to the horizontal reference axes, and determining the intersection point on the earth'"'"''"'"'s surface are combined in the digital computer and said third set of direction cosines is then used in an analog computer to determine from said third set and the direction lines of said second spot with respect to the window axes, the direction of a line from said image viewing point.

7. The invention according to claim 5 wherein computations are done using instantaneous position information.

8. The invention according to claim 5 wherein computations in the analog computer are done by the integration of rate information developed in the digital computer and further including a step to periodically initialize the analog computer.

9. The invention according to claim 8 wherein said initialization step is done for each horizontal scan of said second spot.

10. The invention according to claim 3 wherein said first set of direction cosines and said second set of direction cosines are computed and combined in a digital computer to form a fourth set of direction cosines and said fourth set is then used to reference said direction lines of said second spot to the horizontal axes.

11. The invention according to claim 10 wherein the image is rolled optically and further including the step of determining by computation in the digital computer an image source axes rolled by the amount of image roll and using said axes in determining the direction of said line from said image viewing point.

12. In a display system for presenting to an observer a desired simulated scene of the earth'"'"''"'"'s surface as viewed from the observer'"'"''"'"'s viewpoint, comprising an image source depicting a portion of the earth'"'"''"'"'s surface as viewed from an image viewing point, at least part of which scene contains the same information as that contained in the desired scene;

a device with a controllable first spot for scanning the image source to develop a video signal, a display located within the observer'"'"''"'"'s field of view to form a simulated window through which the observer may view said simulated scene, said display being of the type formed by scanning a second spot across the display to form a raster and modulating said second spot with the video signal developed by said device, apparatus for driving said first spot to obtain an image of the desired scene in proper perspective on said display comprising;

a. means for determining the simulated point of intersection with the earth'"'"''"'"'s surface of a line from the observer passing through the instantaneous position of the second scanning spot on the display window;

b. means for determining the location on the image source of the depicting thereon of said earth intersection point; and

c. means for positioning the first spot so that the video signal developed corresponds to said location on said image source.

13. The invention according to claim 12 wherein said display is used in combination with a fixed-base vehicle trainer and said observer is the trainee.

14. The invention according to claim 13 wherein said trainer is an aircraft simulator.

15. The invention according to claim 12 wherein said image source is a frame of a motion picture and said image source viewing point is the point from which said frame was taken.

16. The invention according to claim 15 wherein said device is a TV camera on which said frame is imaged.

17. The invention according to claim 15 wherein said device is a flying spot scanner, pickup photomultiplier tube and associated optics and wherein said device is arranged to scan said frame.

18. The invention according to claim 12 wherein said image source is the image obtained from an optical probe viewing a model, said model is a portion of the earth'"'"''"'"'s surface and said device is a TV camera on which said image is focused.

19. The invention according to claim 12 wherein said image source is an orthophoto and said device is a flying spot scanner with associated pickup and optics arranged to scan said orthophoto. >