Multi-frequency unwrapping

Patent metadata

Field	Value
Publication number	US-10598783-B2
Application number	US-201615204733-A
Country	US
Kind code	B2
Filing date	Jul 7, 2016
Priority date	Jul 7, 2016
Publication date	Mar 24, 2020
Grant date	Mar 24, 2020

Abstract

The time-of-flight system disclosed herein includes a frequency unwrapping module configured to generate an input phase vector with M phases corresponding to M sampled signals from an object, determine an M−1 dimensional vector of transformed phase values by applying a transformation matrix (T) to the input phase vector, determine an M−1 dimensional vector of rounded transformed phase values by rounding the transformed phase values to a nearest integer, and determine a one dimensional lookup table (LUT) index value by transforming the M−1 dimensional rounded transformed phase values. The index value is input into the one dimensional LUT to determine a range of the object.

First claim

What is claimed is:

1. A physical hardware system to provide multi-frequency unwrapping, comprising:
memory;
one or more processor units;
a light source to generate M signals each being modulated at one of M modulation frequencies;
one or more sensors, each of the sensors to receive reflection of each of the M signals from an object, wherein M is greater than or equal to two;
a signal sampling module configured to generate M sampled signals, each of the M sampled signals corresponding to reflection of one of the M signals; and
a frequency unwrapping module stored in the memory and executable by the one or more processor units, the frequency unwrapping module configured to:
generate an input phase vector with M phases corresponding to the M sampled signals,
determine an M−1 dimensional vector of transformed phase values by applying a transformation matrix (T) to the input phase vector,
determine an M−1 dimensional vector of rounded transformed phase values by rounding the transformed phase values to a nearest integer,
determine a one dimensional lookup table (LUT) index value by transforming the M−1 dimensional rounded transformed phase values,
input the index value into a one dimensional LUT to determine a range of the object, and generate the transformation matrix (T) based upon frequency ratios of the modulation frequencies.

2. The physical hardware system of claim 1 , wherein the frequency unwrapping module is further configured to generate the one dimensional LUT.

3. The physical hardware system of claim 1 , wherein the transformation matrix (T) maps a noiseless phase vector onto an integer lattice.

4. The physical hardware system of claim 1 , wherein the frequency unwrapping module is further configured to generate the one dimensional lookup table (LUT) using the transformation matrix (T) and packing M−1 dimensions into one dimension.

5. The physical hardware system of claim 1 , wherein the one dimensional lookup table (LUT) maps to a phase unwrapping vector (n 1 , n 2 , . . . n M ).

6. The physical hardware system of claim 1 , wherein the frequency unwrapping module is further configured to generate the transformation matrix (T) using a dimensionality reducing matrix (T null ) comprising a plurality of basis vectors orthogonal to a frequency ratio vector (m 1 , m 2 , . . . m M ).

7. The physical hardware system of claim 1 , further comprising a confidence interval calculation module configured to calculate confidence intervals using at least one of:
a. a calculation based on a difference between a final estimated range and a range corresponding to individual unwrapped phase measurements, calculated from θ i +2πn i for the individual unwrapped phase measurement denoted by i, and
b. a calculation based on a difference between a vector of a rounded transformed phase values (r) and an unrounded vector of transformed phase values (v).

8. The physical hardware system of claim 1 , wherein each of the M signals is an amplitude modulated continuous wave laser signal.

9. A method to unwrap range ambiguity in a time-of-flight (TOF) system, the method comprising:
generate M signals each being modulated at one of M modulation frequencies;
illuminating an object with the M signals;
receiving reflection of each of the M signals from the object;
generating M sampled signals, each of the M sampled signals corresponding to reflection of one of the M signals;
generating an input phase vector with M phases corresponding to M sampled signals;
generating a transformation matrix (T) based upon frequency ratios of the modulation frequencies that reduces the dimensionality of the input phase vector from M to M−1 dimensions;
applying the transformation matrix (T) to the input phase vector and rounding to the nearest integer;
determining an index value by mapping the rounded transformed input phase vector from M−1 dimensions to a one dimensional value;
generating a one dimensional lookup table (LUT), wherein the one dimensional LUT provides a plurality of range disambiguations; and
inputting the index value into the one dimensional LUT to determine a range of the object.

10. The method of claim 9 , wherein the range is determined via phase unwrapping of the input phase vector.

11. The method of claim 9 , wherein the transformation matrix (T) maps a noiseless phase vector onto an integer lattice.

12. The method of claim 9 , wherein the one dimensional LUT, is generated using the transformation matrix (T) and comprises packing M−1 dimensions into one dimension.

13. The method of claim 9 , wherein the one dimensional LUT maps to a phase unwrapping vector (n 1 , n 2 , . . . n M ).

14. The method of claim 9 , wherein the transformation matrix (T) is calculated using a dimensionality reducing matrix comprising a plurality of basis vectors orthogonal to a frequency ratio vector (m 1 , m 2 , . . . m M ).

15. The method of claim 9 , where a confidence interval is calculated using at least one of
a. a calculation based on a difference between a final estimated range and a range corresponding to individual unwrapped phase measurements, calculated from θ i +2πn i for the individual unwrapped phase measurement denoted by i, and
b. a calculation based on the difference between the vector of rounded transformed phase values (r) and the unrounded vector of transformed phase values (v).

16. A physical article of manufacture including one or more tangible computer-readable storage media, encoding computer-executable instructions for executing on a computer system a computer process, the instructions comprising:
instructions to generate an input phase vector with M phases corresponding to M sampled signals generated by a signal sampling module configured to generate the M sampled signals, wherein each of the M signals to be modulated at one of M modulation frequencies, wherein the M signals are generated by a light source;
instructions to generate a transformation matrix (T) by combining a dimensionality reducing matrix (T null ) and a deskewing matrix (T deskew );
instructions to determine a transformed input phase vector by applying the transformation matrix (T) to the input phase vector;
instructions to calculate a rounded transformed input phase vector by rounding the transformed input phase vector to the nearest integer;
instructions to generate a one dimensional index value by combining the elements of the rounded transformed input phase vector;
instructions to generate a one dimensional lookup table (LUT) using the transformation matrix (T) and packing M−1 dimensions into one dimension, wherein the one dimensional LUT provides a plurality of range disambiguations; and
instructions to input the one dimensional index value into the one dimensional LUT to determine a range of the object.

17. The physical article of manufacture of claim 16 , further comprising instructions to determine the range by phase unwrapping of the input phase vector.

18. The physical article of manufacture of claim 16 , wherein the transformation matrix (T) maps a noiseless phase vector onto an integer lattice.

Assignees

• Microsoft Technology Licensing Llc

Inventors

• Perry Travis
• Schmidt Mirko
• Godbaz John
• Fenton Michael

Classifications

• G06F17/10

  Complex mathematical operations {(function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544)} · CPC title

• G01S17/89

  for mapping or imaging · CPC title

• G01S7/4915

  Time delay measurement, e.g. operational details for pixel components (signal extraction and conditioning G01S7/493); Phase measurement · CPC title

• G01S17/36 Primary

  with phase comparison between the received signal and the contemporaneously transmitted signal · CPC title

• G01S17/34 Primary

  using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal · CPC title