Passive range measurement apparatus and method

• US 4,695,959 A
• Filed: 08/29/1986
• Issued: 09/22/1987
• Est. Priority Date: 04/06/1984
• Status: Expired due to Fees

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Lees, David E. B., Merchant, John
• Primary Examiner(s): Krass, Errol A.
• Assistant Examiner(s): Black, Thomas G.
• Application Number:
  US06/902,262
• Time in Patent Office: 389 Days
• Field of Search: 364/458, 364/453, 364/562, 342/180, 342/191, 342/197, 342/135, 342/136, 342/138, 356/3, 340/729
• US Class Current: 701/225
• CPC Class Codes: G01C 11/06 by comparison of two or more pictures of the same area

Abstract

A passive range measurement device and method are described which device includes a camera, onboard motion sensors, image digitizers and memories and a digital processor. The device creates a digitized image stream from successive images taken by the camera. The digital processor operates on the image stream in conjunction with information obtained from the onboard motion sensors to determine the location of a median plane through the scene, and the position of terrain detail located on that plane. By evaluating in like fashion hypothetical slices through the scene parallel to the median plane, a topographic range map of the scene may be created. This map is referenced to the position of the camera and platform, and may, therefore, be used to provide a terrain following capability.

Claims

1. A method for passively mapping a desired scene of interest from a first and a second image obtained from a first sensor viewing said scene from a first position and a second position, respectively, said first sensor having a predetermined axis system, said method comprising the method steps of:

A. digitizing said first and second images of said desired scene, thereby creating first and second digitized images, respectively, of said desired scene, each of said digitized images having intensity information which are located at different addresses in a memory;

B. determining the relative position of said first sensor between said first and second positions, respectively, said relative position described by information relating to the rotation of said first sensor about said axis system, the displacement of said first sensor relative to said axis system, and the direction of a normal to a first plane which is substantially coplanar with said scene, said direction measured relative to said axis system;

C. selecting a first range distance along said normal for use in determining the portions of said first image which are positioned on a second plane which is parallel to said first plane substantially at said first range distance from said first sensor;

D. modifying said memory addresses of said intensity information of said second image, thereby producing a first warped image to be used to compare said addresses of said first and second images which have substantially equal intensity information;

E. comparing said first digitized image and said first warped image;

F. extracting the portions of said first image which have a substantially equal intensity with respect to corresponding portions of said first warped image;

G. assigning said first range distance to each of said extracted portions of said first image; and

H. repeating said steps of selecting, modifying, comparing, extracting and assigning for ranges in addition to said first range until the maximum number of addresses having substantially equal intensity values are identified, said extracted image portions and range distances assigned thereto being used to provide a map of the scene of interest.

2. A method as in claim 1 further comprising the step of generating an altitude map of said scene for each of said extracted portions.

3. A method as in claim 1 wherein said mapping method utilizes a second sensor placed at said second position, wherein said first image is sensed by said first sensor placed at said first position, and wherein said second image is sensed by said second sensor.

4. A method for passively mapping a desired scene of interest from a first image and a second image obtained from a first sensor viewing said scene from a first position and a second position, respectively, said first sensor having a fixed axis system, said method comprising the method steps of:

A. digitizing said first and second images of said desired scene, thereby creating first and second digitized images, respectively, of said desired scene, each of said digitized images comprised in an array of two dimensional pixel addresses (x,y), wherein an intensity value f(x,y) is associated with each of said pixel addresses (x,y) in said first image, and wherein an intensity value g(x,y) is associated with each of said pixel addresses (x,y) in said second image;

B. determining the relative position of said first sensor between said first and second positions, said relative position described as follows;

(i) a first matrix describing rotation of said first sensor about said axis system between said first and second positions of said sensor,

(ii) a first vector describing the displacement of said first sensor relative to said axis system, said displacement measured between said first and second positions, and

(iii) a second vector describing, relative to said axis system, a normal to a first plane which is substantially coplanar with said scene of interest;

C. selecting a first range distance R_o for use in determining which of said pixel addresses (x,y) in said first image are positioned substantially on a second parallel to said first plane, said second plane positioned at said range R_o from said first sensor at said first position;

D. computing address modification coefficients a_i,j for said range R_o in order to warp each pixel address (x,y) in said first image to a new pixel address (X,Y) in said second image, wherein said intensity value f(x,y) of said first image is substantially equal to the intensity value g(x,y) of said second image, said computation made in accordance with the following equation;

##EQU9## wherein i and j have the values 1, 2 and 3, respectively, wherein l_i,j is said first matrix, wherein v_i is said first vector; and

wherein L_j is said second vector;

E. warping said second digitized image with said address modification coefficients a_i,j using the following address modification equations;

##EQU10## thereby creating a first warped digitized image comprised in an array of two dimentional pixel addresses (X,Y) wherein an intensity value g(X,Y) is associated with each of said pixel addresses (X,Y) in said first warped digitized image;

F. comparing said first digitized image and said first warped digitized image;

G. extracting said pixel addresses (x,y) in said first digitized image which have said intensity value f(x,y) substantially equal to the intensity value g(X,Y);

H. assigning said first range distance R_o to each of said extracted pixel addresses (x,y);

I. changing said range R_o in order to obtain a new range distance R_x ;

J. repeating said steps of selecting, computing, warping, comparing, extracting, assigning and incrementing for each new range distance R_x ; and

K. generating an altitude map of said scene in the form of a functional value R(x,y), wherein each of said pixel addresses (x,y) in said altitude map R(x,y) corresponds to said pixel addresses (x,y) in said first digitized image, and wherein the functional value R(x,y) is equal to the assigned range values R_o and R_x for each of said extracted pixel addresses (x,y).

5. A method as in claim 4 wherein said method for mapping a desired scene utilizes a second sensor placed at said second position, wherein said first image is sensed by said first sensor placed at said first position, and wherein said second image is sensed by said second sensor.

6. Apparatus for mapping a desired scene of interest from a first and a second image obtained from a first sensor viewing said scene from a first position and a second position, respectively, said first sensor having a predetermined axis system, said apparatus comprising:

A. means for digitizing said first and second images of said desired scene, thereby creating first and second digitized images, respectively, of said desired scene, each of said digitized images having intensity information which are located at different addresses in a memory;

B. means for determining the relative position of said first sensor between said first and second positions, respectively, said relative position described by information relating to the rotation of said first sensor about said axis system, the displacement of said first sensor relative to said axis system, and the direction of a normal, relative to said axis system, to a first plane which is substantially coplanar with said scene;

C. means for selecting a first range distance along said normal for use in determining the portions of said first image which are positioned on a second plane which is parallel to said first plane substantially at said first range distance from said first sensor;

D. means for modifying said memory addresses of said intensity information of said second image, thereby producing a first warped image to be used to compare said addresses of said first and second images which have substantially equal intensity information;

7. E. means for comparing said first digitized image and said first warped image;

F. means for extracting the portions of said first image which have a substantially equal intensity with respect to corresponding portions of said first image;

G. means for assigning said first range distance to each of said extracted portions of said first image;

H. means for enabling said means for determining, selecting, modifying, comparing, extracting and assigning in order to create a high resolution range function of said scene; and

I. means for generating an altitude map of said scene for each of said extracted portions.

9. Apparatus as in claim 7 further comprising means for enabling said means for determining, selecting, computing, comparing and extracting for a plurality of desired ranges R_o in order to create a high resolution range function R(x,y) of said scene.

10. Apparatus as in claim 7 wherein said first means for sensing is positioned at said first postion to sense said first image, and further comprising a second means for sensing positioned at said second position to sense said second image.

11. Apparatus as in claim 7 wherein said means for producing a digital representation of said images further comprises one or more means for storing said digital representations of said digital representations of said images.

12. Apparatus as in claim 7 wherein said means for determining relative position comprises:

A. an inertial motion sensor; and

B. an altimeter.

14. A method for determining a range from a passive sensor to points in a scene as in claim 12 wherein said first plane is a median plane through said scene.

8. Apparatus for passively mapping a desired scene of interest from first and second images of said scene, said images sensed from first and second positions respectively, said apparatus comprising:

A. a first means for sensing, said first means for sensing producing said images of said scene of interest, said first sensor having a predetermined axis system;

B. means for producing a digital representation of said images thereby creating first and second digitized images of said first and second images respectively, each of said images comprised in an array of two dimensional pixel addresses (x,y);

C. means for determining the relative position of said first sensor between said first and second positions, said relative position described as follows;

(i) a first matrix describing rotation of said first sensor about said axis system between said first and second positions,

(ii) a first vector describing the displacement of said first sensor relative to said axis system, said displacement measured between said first and second positions, and

(iii) a second vector describing, relative to said axis system, a normal to a first plane which is substantially coplanar with said scene of interest;

D. means for selecting a first range distance R_o for use in determining which of said pixel addresses (x,y) in said first image are positioned substantially on a second plane parallel to said first plane, said second plane positioned at said range R_o from said first sensor at said first position;

E. means for computing address modification coefficients a_i,j for said range R_o by the equation;

space="preserve" listing-type="equation">a.sub.i,j =l.sub.i,j -(v.sub.i L.sub.j /R.sub.o),

wherein i and j have the values 1, 2 and 3, respectively, l_i,j is said first matrix, v_i is said first vector; and

L_j is said second vector;

F. means for warping said second digitized image with said address modification coefficients a_i,j thereby creating a warped second digitized image comprising an array of two dimensional pixel addresses (X,Y) wherein an intensity value g(X,Y) is associated with each of said pixel addresses (X,Y) in said warped second digitized image;

G. means for comparing said first digitized image and said first warped image;

H. means for extracting said pixel addresses (x,y) in said first digitized image in which said intensity value f(x,y) of said first digitized image is substantially equivalent to the intensity value g(X,Y) of said first warped image;

I. means for producing a range function R(x,y), wherein for each of said extracted pixel addresses (x,y) the value of the function R(x,y) is set to said range R_o ;

J. means for repeating said steps of selecting, computing, warping, comparing, extracting, assigning and incrementing for each new range distance Rhd x; and

K. means for generating an altitude map of said scene in the form of a functional value R(x,y), wherein each of said pixel addresses (x,y) in said altitude map R(x,y) corresponds to said pixel addresses (x,y) in said first digitized image, and wherein the functional value R(x,y) is equal to the assigned range values R_o and R_x for each of said extracted pixel addresses (x,y).

13. A method for determining a range from a passive sensor to points in a scene within the field of view of said sensor, comprising the steps:

A. forming one image of at least a portion of said scene from data acquired by a first passive sensor located at one location, said one image comprised of pixels, each pixel having an address locating said pixel in said scene;

B. forming another image of said portion of said scene from data acquired by a second passive sensor at another location removed from said one location, said another image comprised of pixels, each pixel having an address locating it in said another image;

C. calculating location addresses for pixels in said one image to locate said pixels in a first plane a first distance from said one location;

D. calculating a location address for pixels in said another image to locate said pixels in said first plane;

E. calculating an address for said pixels in said another image to warp said another image into registration with said one image;

F. correlating pixels of said one image and said another image at address locations obtained in steps, c, d, and e;

G. calculating a range to regions of said scene represented by pixels which correlate based on an assumption said regions lie in said first plane.