Method for Enhancing a Three Dimensional Image from a Plurality of Frames of Flash Lidar Data

• US 20120033196A1
• Filed: 06/22/2011
• Published: 02/09/2012
• Est. Priority Date: 03/12/2010
• Status: Active Grant

• Current Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Vanek, Michael D., Amzajerdian, Farzin, Bulyshev, Alexander
• Granted Patent: US 8,494,687 B2
• Time in Patent Office: Days
• US Class Current: 356/4.01
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4808 Evaluating distance, position or velocity data
• CPC Class Codes: G06T 17/05 Geographic models
• CPC Class Codes: G06T 19/00 Manipulating 3D models or images for computer graphics

Abstract

A method for enhancing a three dimensional image from frames of flash LIDAR data includes generating a first distance R_i from a first detector i to a first point on a surface S_i. After defining a map with a mesh Θ having cells k, a first array S(k), a second array M(k), and a third array D(k) are initialized. The first array corresponds to the surface, the second array corresponds to the elevation map, and the third array D(k) receives an output for the DEM. The surface is projected onto the mesh Θ, so that a second distance R_k from a second point on the mesh Θ to the detector can be found. From this, a height may be calculated, which permits the generation of a digital elevation map. Also, using sequential frames of flash LIDAR data, vehicle control is possible using an offset between successive frames.

Claims

1. A method for enhancing a three dimensional image from a plurality of frames of flash LIDAR data, comprising:

(1) emitting laser light from an emitter of a flash LIDAR apparatus to a surface;

(2) capturing light reflected from the surface by a first detector i of the flash LIDAR apparatus;

(3) generating a frame of flash LIDAR data from the captured light, the frame comprising a first distance R_i measured from the first detector i to a first point on the surface S_i;

(4) selecting an elevation map with a mesh Θ

defining a plurality of cells k;

(5) initializing a first array S(k), a second array M(k), and a third array D(k), wherein the first array is associated with the surface, the second array is associated with the elevation map, and the third array D(k) receives an output comprising an output elevation map for the mesh Θ

;

(6) projecting the surface onto a reference surface Ω

to create a projection, wherein the projection comprises a zero elevation level;

(7) selecting a set of cells from the mesh Θ

that overlaps with the projection;

(8) calculating a second distance R_k from a second point on the mesh Θ

to the detector, wherein a location of the second point corresponds with a location of the first point;

(9) calculating a height h_ki, between the first point and the second point according to the equation

h_ki=(R_kR_i)×

sin θ

_i,

wherein θ

_i is an angle between the surface and the reference surface Ω

;

(10) updating the first and second arrays according to the equations

S(k₁)=S(k₁)+h_k1

M(k₁)+M(k₁)+1;

(11) after completing the updating for all detectors i in the frame of flash LIDAR data, normalizing according to the equation

D(k)=S(k)/M(k) for all k

thereby calculating the third array D(k);

(12) repeating steps (6) through (11) for each subsequent frame of LDAR data.

2. The method of claim 1, wherein the first point and the second point are a center points that are vertically aligned with one another.

3. The method of claim 1, wherein the first distance R_i comprises a plurality of distances, and the second distance R_k comprises a plurality of distances.

4. The method of claim 1, wherein the first array S(k), the second array M(k), and the third array D(k) are initialized by zeroing the values therein.

5. The method of claim 1, wherein the plurality of cells k define an array of A×

B pixels.

8. The method of claim 1, wherein the range R_i is calculated according the equation

9. The method of claim 2, further comprising the step of:

(14) determining a vector of state for the flash LIDAR apparatus according to the following equation

T(V_n+1)−

T(V_n)=R_n+1−

R_n

wherein T(V) is a function of the vector of state, wherein the first detector comprises a first plurality of pixels having a plurality of first distances measured from the first plurality of pixels to a plurality of first points on the surface S_i, wherein R_n is a matrix comprising the plurality of first distances, wherein the second detector comprises a second plurality of pixels having a plurality of second distances measured from the second plurality of pixels to a plurality of second points on the surface S_i, wherein R_n+1 is a matrix comprising the plurality of second distances.

10. The method of claim 9, further comprising the step of:

(15) solving a linear approximation equation as follows;

11. The method of claim 10, further comprising the steps of:

(17) applying 2-D discrete Fourier transform to the elevation map;

(18) applying regularized inverse filter to the elevation map;

(19) applying inverse 2-D discrete Fourier transform to the elevation map;

(20) improving the spatial resolution of the elevation map.

12. The method of claim 9, further comprising the step of (15) solving an internal inerative equation as follows:

V₂^k=V₁+(B⁺B)<sup>−

1</sup>×

(R(V₂<sup>k−

1</sup>,h)−

T₂), k=1, . . . , N

V₂⁰=V₁

(16) updating the elevation map.

13. The method of claim 12, further comprising the steps of:

(17) applying 2-D discrete Fourier transform to the elevation map;

(18) applying regularized inverse filter to the elevation map;

(19) applying inverse 2-D discrete Fourier transform to the elevation map;

(20) improving the spatial resolution of the elevation map.

7. The method of claim 7, wherein the array is a rectangular array, with A>

B.

6. The method of claim 7, wherein the array is a square array, with A=B.

14. A method for enhancing a three dimensional image from a plurality of frames of flash LIDAR data in real time, comprising:

(1) emitting laser light from an emitter of a flash LIDAR apparatus to a surface;

(2) capturing light reflected from the surface by a first detector i of the flash LIDAR apparatus;

(3) generating a frame of flash LIDAR data from the captured light, the frame comprising a first distance R_i measured from the first detector i to a first point on the surface S_i;

(4) selecting an elevation map with a mesh Θ

defining a plurality of cells k;

(5) initializing a first array S(k), a second array M(k), and a third array D(k), wherein the first array is associated with the surface, the second array is associated with the elevation map, and the third array D(k) receives an output comprising an output elevation map for the mesh Θ

;

(6) projecting the surface onto a reference surface Ω

to create a projection;

(7) selecting a set of cells from the mesh Θ

that overlaps with the projection;

(8) calculating a second distance R_k from a second point on the mesh Θ

to the detector, wherein a location of the second point corresponds with a location of the first point;

(9) calculating a height h_ki between the first point and the second point according to the equation

h_ki=(R_k−

R_i)×

sin θ

_i,

wherein θ

_i is an angle between the surface and the reference surface Ω

;

(10) updating the first and second arrays according to the equations

S(k₁)=S(k₁)+h_k1

M(k₁)=M(k₁)+1;

(11) after completing the updating for all detectors i in the frame of flash LIDAR data, normalizing according to the equation

D(k)=S(k)/M(k) for all k

thereby calculating the third array D(k); and

(12) repeating steps (6) through (11) for a frame of LIDAR data.

15. The method of claim 14, further comprising the steps of (13) providing an avionic device, wherein the third array D(k) is provided as input to the avionic device to provide guidance, navigation, and control.

16. The method of claim 15, wherein the avionic device comprises a Kalman filter.

17. The method of claim 16, wherein steps 1 through 12 are repeated 30 times within 1 second.

18. The method of claim 17, wherein the three dimensional image is image is enhanced such that a four centimeter object can be detected from one kilometer distance with a flash LIDAR.

19. A method for enhancing a three dimensional image from a plurality of frames of flash LIDAR data, comprising:

(1) emitting laser light from an emitter of a flash LIDAR apparatus to a surface;

(2) capturing light reflected from the surface by a first detector i of the flash LIDAR apparatus;

(3) generating a frame of flash LIDAR data from the captured light, the frame comprising a first distance R₁ measured from the first detector i to a first point on the surface S_i;

(4) selecting an elevation map with a mesh Θ

defining a plurality of cells k;

(5) initializing a first array S(k), a second array M(k), and a third array D(k), wherein the first array is associated with the surface, the second array is associated with the elevation map, and the third array D(k) receives an output comprising an output elevation map for the mesh Θ

;

(6) projecting the surface onto a reference surface Ω

to create a projection;

(7) selecting a set of cells from the mesh Θ

that overlaps with the projection;

(8) calculating a second distance R_k from a second point on the mesh Θ

to the detector, wherein a location of the second point corresponds with a location of the first point;

(9) calculating a height k_ki between the first point and the second point according to the equation

h_ki=(R_k−

R_i)×

sin θ

_i,

wherein θ

_i is an angle between the surface and the reference surface Ω

, wherein the range R_i is calculated according the equation

20. A vehicle that operates according to the method of claim 19, and wherein the third array D(k) is provided as input to a guidance, navigation, and control processor for navigation of the vehicle.