Methods and systems for hierarchical de-aliasing time-of-flight (TOF) systems
View Patent ↗A TOF system acquires depth data using n≧3 modulation frequencies f 1 , f 2 , . . . , f m separately, associated with separate aliasing interval ranges Z 1 , Z 2 , . . . , Z m . Next, n intermediate frequencies f DE1 , f DE2 , . . . , f DEn are generated sorted by order of f DE1 <f DE2 < . . . <f DEn and corresponding phases are computed from the data acquired separately using f 1 , f 2 , . . . , f m . Hierarchically dealiasing of the thus-acquired data is carried out using the generated intermediate frequencies. Hierarchical dealiasing may be carried out one step at a time, if desired. Thus operated, the TOF system provides an effective aliasing interval range Z D >Z k for k=1 . . . n as if said TOF system operated at a very low modulation frequency f D , while simultaneously providing depth resolution certainty as if said TOF system operated at a high modulation frequency f E . Preferably high modulation frequency f E is a function of all modulation frequencies f 1 , f 2 , . . . , f m , which function may be an arithmetic mean or a weighted average of f 1 , f 2 , . . . , f m .
1. A processor implemented method to hierarchically dealias distance Z range of a phase-type time of flight system having a processor, the method comprising:
(a) acquiring data from said time of flight system using modulation frequencies f 1 , f 2 , . . . , f m separately, wherein if said time of flight time of flight system were operated solely at one of said modulation frequencies, aliasing interval ranges of Z 1 , Z 2 , . . . , Z m would result;
(b) generating n intermediate frequencies f DE1 , f DE2 , . . . , f DEn sorted by order of f DE1 <f DE2 < . . . <f DEn and computing their corresponding phases from data acquired at step (a); and
(c) hierarchically dealiasing data acquired at step (a) using said intermediate frequencies generated at step (b);
wherein said time of flight system provides an effective aliasing interval range Z D >Z k for k=1 . . . n as if said time of flight system operated at a very low modulation frequency f D , while simultaneously providing depth resolution certainty as if said time of flight system operated at a high modulation frequency f E .
2. The method of claim 1 , wherein at step (b), selection of said intermediate frequency f DE1 , f DE2 , . . . , f DEn is based on a ratio between two frequencies
f
DE
(
k
+
1
)
f
DEk
,
which is limited by a ratio determined by an uncertainty requirement.
3. The method of claim 1 , wherein at step (c), hierarchical dealiasing is done one step at a time.
4. The method of claim 3 , wherein at step (c) includes first dealiasing phase data of f DE1 using phase of f D , and then dealiasing phase of f DE2 using phase of f DE1 .
5. The method of claim 4 , wherein at each step phase of f DE(k+1) is dealiased using phase of f DEk until a last step, at which phase f E is dealiased using phase of f DEn to yield unwrapped phase of f E .
6. The method of claim 1 , wherein f E is a function of all modulation frequencies f 1 , f 2 , . . . , f m , said function selected from at least one of (i) an arithmetic mean of f 1 , f 2 , . . . , f m , and (ii) a weighted average of f 1 , f 2 , . . . , f m .
7. The method of claim 1 , wherein unwrapped phase of f E is computable as follows:
(i) at a last step of hierarchical de-aliasing, dealiasing phase of each said modulation frequency f 1 , f 2 , . . . , f m using f DEn to get unwrapped phase of each modulation frequency; and
(ii) computing unwrapped phase of f E using a function between f E and f 1 , f 2 , . . . , f m .
8. The method of claim 1 , wherein at each step of dealiasing phase of f DE(k+1) using phase of f DEk , a corrected phase cycle of f DEk within the [0, 2π] cycle of f DE(k−1) from a previous, de-aliasing step is used to find a correct phase cycle of f DE(k+1) within a cycle of f DEk ;
wherein correct cycle of f DE(k+1) within a total unambiguous range Z D , or the cycle of f D can be found.
9. The method of claim 1 , wherein said method is carried out by said time of flight system.
10. A hierarchical dealiasing unit useable with a phase-based time of flight system, the hierarchical dealiasing unit including a memory and a processor and comprising:
code instructing the processor to cause said time of flight system to acquire data using modulation frequencies f 1 , f 2 , . . . , f m separately, wherein if said time of flight system were operated solely at one of said modulation frequencies, aliasing interval ranges of Z 1 , Z 2 , . . . , Z m would result;
code instructing the processor to generate n intermediate frequencies f DE1 , f DE2 , . . . , f DEn sorted by order of f DE1 <f DE2 < . . . <f DEn and computing their corresponding phases from data acquired at step (a); and
code instructing the processor to hierarchically dealias data acquired using said modulation frequencies f 1 , f 2 , . . . , f m separately using said n intermediate frequencies f DE1 , f 2 , . . . f DEn ;
wherein said time of flight system provides an effective aliasing interval range Z D >Z k for k=1 . . . n as if said time of flight system operated at a very low modulation frequency f D , while simultaneously providing depth resolution certainty as if said time of flight system operated at a high modulation frequency f E .
11. The hierarchical dealiasing unit of claim 10 , wherein code instructing the processor to generate selects said intermediate frequency f DE1 , f DE2 , . . . , f DEn based on a ratio between two frequencies
f
DE
(
k
+
1
)
f
DEk
,
which is limited by a ratio determined by an uncertainty requirement.
12. The hierarchical dealiasing unit of claim 10 , wherein hierarchical dealiasing is done one step at a time.
13. The hierarchical dealiasing unit of claim 10 , wherein there first occurs dealiasing phase data of f DE1 using phase of f D , followed by dealiasing phase of f DE2 using phase of f DE1 .
14. The hierarchical dealiasing unit of claim 12 , wherein at each step phase of f DE(k+1) is dealiased using phase of f DEk until a last step, at which phase f E is dealiased using phase of f DEn to yield unwrapped phase of f E .
15. The hierarchical dealiasing unit of claim 10 , wherein f E is a function of all modulation frequencies f 1 , f 2 , . . . , f m , said function selected from at least one of (i) an arithmetic mean of f 1 , f 2 , . . . , f m , and (ii) a weighted average of f 1 , f 2 , . . . , f m .
16. The hierarchical dealiasing unit of claim 10 , wherein:
unwrapped phase of f E is computable by, at a last step of hierarchical de-aliasing, dealiasing phase of each said modulation frequency f 1 , f 2 , . . . , f m using f DEn to get unwrapped phase of each modulation frequency; and computing unwrapped phase of f E using a function between f E and f 1 , f 2 , . . . , f m .
17. The hierarchical dealiasing unit of claim 10 , wherein at each step of dealiasing phase of f DE(k+1) using phase of f DEk , a corrected phase cycle of f DEk within the [0,2π] cycle of f DE(k−1) from a previous de-aliasing step is used to find a correct phase cycle of f DE(k+1) within a cycle of f DEk ;
wherein correct cycle of f DE(k+1) within a total unambiguous range Z D , or the cycle of f D can be found.
18. A phase-based time-of-flight system including a processor implementing a hierarchical dealiasing unit, said hierarchical dealiasing unit comprising:
a sensor responsive to the processor and causing said time of flight system to acquire data using modulation frequencies f 1 , f 2 , . . . , f m separately, wherein if said time of flight system were operated solely at one of said modulation frequencies, aliasing interval ranges of Z 1 , Z 2 , . . . , Z in would result;
a clock interface component for generating n intermediate frequencies f DE1 , f DE2 , . . . , f DEn sorted by order of f DE1 <f DE2 < . . . <f DEn and computing their corresponding phases from data acquired at step (a); and
the processor hierarchically dealiasing data acquired using said modulation frequencies f 1 , f 2 , . . . , f m separately using said n intermediate frequencies f DE1 , f DE2 , . . . , f DEn ;
wherein said time of flight system provides an effective aliasing interval range Z D >Z k for k=1 . . . n as if said time of flight system operated at a very low modulation frequency f D , while simultaneously providing depth resolution certainty as if said time of flight system operated at a high modulation frequency f E .
19. The time of flight system of claim 18 , wherein said clock interface component selects said intermediate frequency f DE1 , f DE2 , . . . , f DEn based on a ratio between two consecutive frequencies f DE(k+1) which is limited by a ratio determined by an uncertainty requirement.
20. The time of flight system of claim 18 , wherein said hierarchical dealiasing unit has at least one characteristic selected from a group consisting of (i) hierarchical dealiasing is done one step at a time, (ii) there first occurs dealiasing phase data of f DE1 using phase of f D , followed by dealiasing phase of f DE2 using phase of f DE1 , (iii) at each step phase of f DE(k+1) is dealiased using phase of f DEk until a last step, at which phase f E is dealiased using phase of f DEn to yield unwrapped phase of f E , (iv) f E is a function of all modulation frequencies f 1 , f 2 , . . . , f m said function selected from at least one of (i) an arithmetic mean of f 1 , f 2 , . . . , f m , and (ii) a weighted average of f 1 , f 2 , . . . , f m , (v) unwrapped phase of f E is computable by, at a last step of hierarchical de-aliasing, dealiasing phase of each said modulation frequency f 1 , f 2 , . . . , f m using f DEn to get unwrapped phase of each modulation frequency; and computing unwrapped phase of f E using a function between f E and f 1 , f 2 , . . . , f m , and (vi) at each step of dealiasing phase of f DE(k+1) using phase of f DEk , a corrected phase cycle of f DEk within the [0, 2π] cycle of f DE(−1) from a previous de-aliasing step is used to find a correct phase cycle of f DE(k+1) within a cycle of f DEk such that correct cycle of f DE(k+1) within a total unambiguous range Z D , or the cycle of f D can be found.