Distance Determination Using Multi-Wavelength Phase Unwrapping
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Solution Overview
Problem
Current distance measuring technologies using time-of-flight (TOF) methods face limitations in unambiguity range and are prone to measurement noise, especially when using single-frequency systems, which restricts the usable distance measurement range and increases computational effort when employing multiple frequencies.
Innovation Solution
A method that provides phase measurements made with modulated light at different wavelengths, involves generating possible wraparound count combinations, determining unwrapped phase hypotheses for each combination, and selecting the most plausible combination based on variance or standard deviation to estimate the distance accurately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If multiple modulation frequencies are used to extend the distance measurement range, then the usable distance measurement range is improved, but the computational effort increases
Solution Approach 1:
The patent segments the phase unwrapping problem by processing pixels in groups rather than individually. By dividing the scene into groups of neighboring pixels and performing phase unwrapping on each group simultaneously, the computational complexity is reduced from O(N) to O(N/k) where k is the group size, while still achieving the extended measurement range benefits of multi-frequency operation
Solution Approach 2:
The patent performs preliminary classification of pixels into wrapped and unwrapped states based on phase differences before performing the actual phase unwrapping operation. This preliminary action identifies which pixels require unwrapping and prepares the data structure in advance, reducing the computational effort during the main processing stage
2Measurement precision
If phase unwrapping is performed to retrieve actual distance from ambiguous measurements, then measurement accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent extracts only the necessary phase difference information between neighboring pixels to determine wraparound counts, rather than performing complete phase unwrapping on all pixels. By taking out only the essential information needed for accurate distance retrieval, the computational complexity is significantly reduced while maintaining measurement precision
Solution Approach 2:
The patent performs partial phase unwrapping by focusing computational resources on pixels that are likely to be wrapped based on phase difference thresholds, rather than uniformly processing all pixels. This selective approach achieves sufficient measurement accuracy for most pixels while reducing overall computational complexity
3Device complexity
If assumptions on scene smoothness are made to simplify single-frequency operation, then device complexity is reduced, but measurement reliability deteriorates
Solution Approach 1:
The patent introduces phase difference analysis between neighboring pixels as an intermediary step that bridges the gap between simple single-frequency operation and accurate multi-frequency measurement. By using phase differences as a mediator to identify wrapped pixels, the system achieves reliable measurements without requiring strong assumptions about scene smoothness
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively extends the usable distance measurement range and reduces computational complexity by selecting the most plausible combination of unwrapped phase hypotheses, enhancing accuracy and efficiency in distance estimation even in the presence of noise.
Implementation Method 1
Distance measuring equipment often relies on the time-of-flight (TOF) measurement principle. Distance (also: depth) information is in this case obtained by emitting modulated light into the direction of the target and measuring the phase shift of the modulation between the emitted and the reflected light.
Data Source
AI summary
A method for determining a distance comprises: providing at least two phase measurements made with modulated light of different modulation wavelengths, each phase measurement being indicative of the distance up to an integer multiple of a respective modulation wavelength; providing a set of possible wraparound count combinations; for each one of the possible wraparound count combinations, calculating a combination of unwrapped phase hypotheses corresponding to the at least two phase measurements; and selecting a most plausible combination of unwrapped phase hypotheses among the combinations of unwrapped phase hypotheses and calculating the distance based upon the selected most plausible combination of unwrapped phase hypotheses.