Distance determination method

1. A method for determining a distance between a time-of-flight (TOF) measuring device and a target, wherein the time-of-flight measuring device is configured to generate a range image of the target and includes an illumination unit, an imaging sensor, and an evaluation unit coupled with a non-transitory memory, the method comprising:

defining a usable distance measurement range within which the TOF measuring device determines a distance to the target;

generating a table containing all possible wraparound count combinations for phase measurements at different modulation frequencies, wherein the table is stored in the non-transitory memory as part of the TOF measuring device configuration;

emitting light from the illumination unit into a direction of the target, wherein the light is modulated at different modulation wavelengths;

receiving at the imaging sensor the modulated light reflected from the target and generating a phase information signal based on the reflected light at the different modulation wavelengths;

using the evaluation unit, determining for each pixel of the imaging sensor, phase measurements based on the phase information signal received from the imaging sensor, wherein each phase measurement is indicative of the distance up to an integer multiple of a respective modulation wavelength;

using the evaluation unit, for each one of the possible wraparound count combinations in the table, determining a combination of unwrapped phase hypotheses based on the phase measurements;

using the evaluation unit, determining a most plausible combination of unwrapped phase hypotheses among the combinations of unwrapped phase hypotheses

by calculating, for each combination of unwrapped phase hypotheses, a gap between a point having the respective unwrapped phase hypotheses as coordinates and an origin-crossing straight line having a direction vector with coordinate representation [c/λ 1 , . . . , c/λ n ], where λ 1 , . . . , λ n designate the different modulation wavelengths and c designates the speed of light, and selecting as the most plausible combination of unwrapped phase hypotheses the one for which the gap is smallest;

calculating the distance to the target for each pixel of the image sensor based on the selected most plausible combination of unwrapped phase hypotheses; and

generating a range image of the target using the distance calculated for each pixel.

2. The method as claimed in claim 1 , wherein the distance is determined as



φ

→

est

′



·

c

4

⁢

π

·



u

→



,

where {right arrow over (φ)}′ est is an orthogonal projection onto the origin-crossing straight line of a point having the most plausible combination of unwrapped phase hypotheses as coordinates, and it is the direction vector [c/λ 1 , . . . , c/λ n ].

3. The method as claimed in claim 1 , wherein the determining of the gap is carried out in a rotated coordinate system, in which the origin-crossing straight line is a coordinate axis.

4. The method as claimed in claim 3 , wherein the distance is determined as

(

φ

→

j_opt

″

)

1

·

c

4

⁢

π

·



u

→



where ({right arrow over (φ)}″ j_opt ) 1 is a coordinate of said point having the most plausible combination of unwrapped phase hypotheses as coordinates in the rotated coordinate system, and {right arrow over (u)} is the direction vector [c/λ 1 , . . . , c/λ n ].

5. A computer program product, stored on a non-transitory computer readable medium, the computer program product comprising computer-implementable instructions, which, when executed by a processing unit, cause the processing unit to carry out the method as claimed in claim 1 .

6. Time-of-flight distance measuring device, comprising:

an electronic control unit coupled to a memory,

the memory having stored therein a computer program as claimed in claim 5 ,

the electronic control unit being configured to execute the computer program when determining a distance,

wherein the electronic control unit is the processing unit.

7. Time-of-flight distance measuring device, comprising:

an electronic control unit with an FPGA and/or an ASIC, said FPGA and/or ASIC configured and arranged to carry out the method as claimed in claim 1 .

8. The method as claimed in claim 1 , wherein the usable distance measurement range is less than a target detection range of the TOF measuring device.

9. The method as claimed in claim 1 , further comprising determining whether the distance is a valid distance that lies within the usable distance measurement range based on a comparison of the smallest gap to a minimum line segment distance value.