Depth sensing using line pattern generators
A distance measurement system includes two or more line pattern generators (LPGs), a camera, and a processor. Each LPG emits a line pattern having a first set of dark portions separated by a respective first set of bright portions. A first line pattern has a first angular distance between adjacent bright portions, and a second line pattern has a second angular distance between adjacent bright portions. The camera captures at least one image of the first line pattern and the second line pattern. The camera is a first distance from the first LPG and a second distance from the second LPG. The processor identifies a target object illuminated by the first and second line patterns and determines a distance to the target object based on the appearance of the target object as illuminated by the first and second line patterns.
1. A system for measuring a distance to an object, the system comprising:
a first pattern generator configured to emit a first pattern, the first pattern having a first angular distance between adjacent bright portions in the first pattern;
a second pattern generator configured to emit a second pattern, the second pattern having a second angular distance between adjacent bright portions in the second pattern; and
a processor configured to:
receive at least one image of the first pattern and the second pattern;
identify, in the at least one image, a target object illuminated by the first pattern and the second pattern,
identify, in the at least one image, a background illuminated by the first pattern and the second pattern,
determine a first phase difference between the target object illuminated by the first pattern and the background illuminated by the first pattern,
determine a second phase difference between the target object illuminated by the second pattern and the background illuminated by the second pattern, and
calculate a distance to the target object based on the first phase difference and the second phase difference.
2. The system of claim 1 , wherein the at least one image of the first pattern and the second pattern comprises a first image of the first pattern and a second image of the second pattern.
3. The system of claim 2 , wherein the processor is configured to:
determine the first phase difference in the first image, the first phase difference
describing a difference in phase between a first portion of the first pattern projected on the target object and a second portion of the first pattern projected on the background;
determine the second phase difference in the second image, the second phase difference describing a difference in phase between a first portion of the second pattern projected on the target object and a second portion of the second pattern projected on the background.
4. The system of claim 1 , wherein calculating the distance to the target object comprises calculating L according to the following equation:
Δα
=
(
2
π
b
1
δφ
1
-
2
π
b
2
δφ
2
)
(
L
-
1
-
L
0
-
1
)
wherein Δα is the difference between the first phase difference and the second phase difference, b 1 is a first distance from the first pattern generator to a camera, b 2 is a second distance from the second pattern generator to the camera, δφ 1 is the first angular distance, δφ 2 is the second angular distance, and L 0 is a distance to the background.
5. The system of claim 1 , wherein the first pattern generator comprises a light source and a first grating assembly, the second pattern generator comprises the same light source and a second grating assembly, and the first angular distance is different from the second angular distance.
6. The system of claim 1 , wherein the first pattern generator comprises a first light source and a first grating, the second pattern generator comprises a second light source and a second grating.
7. The system of claim 1 , wherein the first pattern comprises a series of horizontal or vertical lines separated by the first angular distance, and the second pattern comprises a series of horizontal or vertical lines separated by the second angular distance.
8. The system of claim 1 , wherein the first pattern comprises a first grid with a first plurality of dots, wherein adjacent dots in a first direction across the first grid are separated by the first angular distance, and the second pattern comprises a second grid with a second plurality of dots, wherein adjacent dots in a second direction across the second grid are separated by the second angular distance.
9. The system of claim 1 , wherein the first pattern comprises a first set of concentric circles with two adjacent circles separated by the first angular distance, and the first pattern comprises a second set of concentric circles with two adjacent circles separated by the second angular distance.
10. A method for measuring a distance to an object, the method comprising:
receiving at least one image of a target object illuminated by a first pattern and a second pattern, the first pattern emitted by a first pattern generator and the first pattern having a first angular distance between adjacent bright portions in the first pattern, and the second pattern emitted by a second pattern generator and the second pattern having a second angular distance between adjacent bright portions in the second pattern;
identifying, in the at least one image, the target object illuminated by the first pattern and the second pattern;
identifying, in the at least one image, a background illuminated by the first pattern and the second pattern;
determining a first phase difference between the target object illuminated by the first pattern and the background illuminated by the first pattern;
determining a second phase difference between the target object illuminated by the second pattern and the background illuminated by the second pattern; and
calculating a distance to the target object based on the first phase difference and the second phase difference.
11. The method of claim 10 , wherein the at least one image of the first pattern and the second pattern comprises a first image of the first pattern and a second image of the second pattern, and calculating the distance to the target object comprises:
determining the first phase difference in the first image, the first phase difference describing a difference in phase between a first portion of the first pattern projected on the target object and a second portion of the first pattern projected on the background; and
determining the second phase difference in the second image, the second phase difference describing a difference in phase between a first portion of the second pattern projected on the target object and a second portion of the second pattern projected on the background.
12. The method of claim 10 , wherein calculating the distance to the target object comprises calculating L according to the following equation:
Δα
=
(
2
π
b
1
δφ
1
-
2
π
b
2
δφ
2
)
(
L
-
1
-
L
0
-
1
)
wherein Δα is the difference between the first phase difference and the second phase difference, b 1 is a first distance from the first pattern generator to a camera, b 2 is a second distance from the second pattern generator to the camera, δφ 1 is the first angular distance, δφ 2 is the second angular distance, and L 0 is a distance to the background.
13. The method of claim 10 , further comprising:
instructing the first pattern generator to emit the first pattern;
instructing the second pattern generator to emit the second pattern; and
instructing a camera to capture the at least one image.
14. The method of claim 10 , wherein the first pattern comprises a series of horizontal or vertical lines separated by the first angular distance, and the second pattern comprises a series of horizontal or vertical lines separated by the second angular distance.
15. The method of claim 10 , wherein the first pattern comprises a first grid with a first plurality of dots, wherein adjacent dots in a first direction across the first grid are separated by the first angular distance, and the second pattern comprises a second grid with a second plurality of dots, wherein adjacent dots in a second direction across the second grid are separated by the second angular distance.
16. The method of claim 10 , wherein the first pattern comprises a first set of concentric circles with two adjacent circles separated by the first angular distance, and the first pattern comprises a second set of concentric circles with two adjacent circles separated by the second angular distance.
17. A non-transitory computer readable medium storing instructions for measuring a distance to an object, the instructions, when executed by a processor, cause the processor to:
receive at least one image of a target object illuminated by a first pattern and a second pattern, the first pattern emitted by a first pattern generator and the first pattern having a first angular distance between adjacent bright portions in the first pattern, and the second pattern emitted by a second pattern generator and the second pattern having a second angular distance between adjacent bright portions in the second pattern;
identify, in the at least one image, the target object illuminated by the first pattern and the second pattern;
identify, in the at least one image, a background illuminated by the first pattern and the second pattern;
determine a first phase difference between the target object illuminated by the first pattern and the background illuminated by the first pattern;
determine a second phase difference between the target object illuminated by the second pattern and the background illuminated by the second pattern; and
calculate a distance to the target object based on the first phase difference and the second phase difference.
18. The non-transitory computer readable medium of claim 17 , wherein the instructions further cause the processor to:
instruct the first pattern generator to emit the first pattern;
instruct the second pattern generator to emit the second pattern; and
instruct a camera to capture the at least one image.
19. The non-transitory computer readable medium of claim 17 , wherein the first pattern comprises a series of horizontal or vertical lines separated by the first angular distance, and the second pattern comprises a series of horizontal or vertical lines separated by the second angular distance.
20. The non-transitory computer readable medium of claim 17 , wherein the first pattern comprises one of a grid with a plurality of dots, wherein adjacent dots in a first direction across the grid are separated by the first angular distance; and a set of concentric circles with two adjacent circles separated by the first angular distance.