Stereo 3D Measurement Using Temporal Pattern Coding
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Solution Overview
Problem
Current three-dimensional object measurement methods using stereoscopy face challenges in robustness and susceptibility to interference, particularly in industrial environments, due to difficulties in finding correspondences between images from different cameras and limitations in precise indexing and depth determination.
Innovation Solution
The method employs a combination of two-dimensional and temporal coding, using intrinsically and extrinsically calibrated cameras to project and record patterns, which allows for robust correspondence finding and measurement by correlating areal and temporal coding, thereby increasing accuracy and reducing interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If uncoded lines of light are projected onto the object with a large triangulation angle, then depth determination precision is improved, but line indexing becomes difficult and measurement reliability deteriorates
Solution Approach 1:
The patent applies temporal coding where different lines are illuminated with different temporal patterns (bright/dark sequences) to enable unique identification. Each line has a distinct temporal signature that allows reliable indexing even with large triangulation angles, resolving the contradiction between depth precision and indexing reliability.
Solution Approach 2:
The patent uses periodic temporal coding patterns where lines are illuminated in repeating bright/dark sequences. This periodic action creates distinguishable temporal signatures for each line, enabling reliable correspondence matching and indexing while maintaining large triangulation angles for precise depth measurement.
2Reliability
If multiple cameras with different triangulation angles are used, then measurement robustness is improved, but system complexity and data processing burden increase
Solution Approach 1:
The patent replaces the mechanical approach of using multiple cameras with different triangulation angles with a computational approach using temporal coding. A single camera with temporally coded illumination can achieve the same measurement robustness, reducing system complexity while maintaining reliability.
Solution Approach 2:
The patent changes the illumination parameter from spatial variation (multiple cameras) to temporal variation (coded illumination sequences). This parameter change allows a single camera system to achieve robust measurements through temporal discrimination, reducing device complexity while maintaining measurement reliability.
3Measurement precision
If dense line patterns are projected for high resolution, then measurement precision is improved, but correspondence matching between cameras becomes more difficult
Solution Approach 1:
The patent uses temporal coding where each line in the dense pattern is assigned a unique temporal pattern. This allows high-resolution dense line patterns to be projected while maintaining easy correspondence matching, as each line's temporal signature provides unambiguous identification regardless of pattern density.
Data Source
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AI summary
The invention relates to a method and a system for measuring an object (2) by means of stereoscopy, in which method a pattern (3) is projected onto the object surface by means of a projector (9) and the pattern (3), which is designated as a scene and is projected onto the object surface, is captured by at least two cameras (4.1, 4.2, 4.3, 4.4), wherein correspondences of the scene are found in the images captured by the cameras (4.1, 4.2, 4.3, 4.4) by means of a computing unit (5) using image processing, and the object (2) is measured by means of the correspondences found. According to the invention, the cameras (4.1, 4.2, 4.3, 4.4) are intrinsically and extrinsically calibrated, and a two-dimensional and temporal coding is generated during the pattern projection, by (a) projecting a (completely) two-dimensionally coded pattern (3) and capturing the scene using the cameras (4.1, 4.2, 4.3, 4.4), and (b) projecting a temporally encoded pattern having a two-dimensionally different coding several times in succession and using the cameras (4.1, 4.2, 4.3, 4.4) to capture several scenes in succession, the capturing of said scenes being triggered simultaneously in each case.