Optical Measurement Calibration via Correlation Field Rectification
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for calibrating optical measurement setups with high particle concentrations in three-dimensionally extended measurement volumes are inefficient due to the need for unambiguous particle identification and triangulation, which is not feasible at higher concentrations and leads to increased 'ghost particles', and are not suitable for precise corrections in dynamic environments.
Innovation Solution
A method involving simultaneous mapping of the measurement volume by cameras, rectification of camera images relative to a common reference plane, two-dimensional correlation of rectified images to produce correlation fields, reduction of these fields to a straight line, and using the distance from the coordinate origin as correction values for the mapping functions, eliminating the need for explicit particle identification and triangulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If triangulation methods are used for calibration correction, then mapping function accuracy is improved, but the method becomes infeasible with high particle concentrations due to increased ghost particles
Solution Approach 1:
The patent extracts the calibration correction process from the traditional triangulation method that requires particle identification. Instead of identifying and correlating individual particles across cameras, the method extracts correlation information directly from the entire camera images through image correlation techniques, eliminating the need for particle identification while achieving mapping function correction
Solution Approach 2:
The patent introduces image correlation as an intermediary method between the cameras and the mapping function correction. Rather than directly using particle positions (which become unreliable at high concentrations), the method uses correlation fields derived from image patterns as an intermediary to determine calibration corrections, bypassing the ghost particle problem
2Ease of manufacture
If pre-calibration is performed with calibration plates, then initial mapping functions are obtained, but additional correction is required due to mechanical instabilities and vibrations
Solution Approach 1:
The patent implements a feedback mechanism where the system performs self-calibration using its own measurement capability. By correlating images from multiple cameras and analyzing correlation fields, the system continuously monitors and corrects its mapping functions, creating a closed-loop feedback system that compensates for mechanical instabilities and vibrations occurring between pre-calibration and measurement
Solution Approach 2:
The patent enables the measurement system to perform its own calibration correction without external intervention or additional hardware. The system uses its existing camera setup and image processing capability to automatically detect and correct mapping function deviations, making the calibration process self-service and eliminating the need for repeated pre-calibration procedures
3Measurement precision
If volumetric self-calibration is performed multiple times, then mapping functions are corrected, but computational intensity increases
Solution Approach 1:
The patent extracts the essential calibration information from correlation fields by reducing them to correlation maxima bands and then to specific distance measurements. This extraction process identifies only the critical information needed for correction (the distance of correlation maxima from the coordinate origin), eliminating unnecessary computational steps while preserving correction accuracy
Solution Approach 2:
The patent applies partial action by performing correction based on correlation fields from selected camera pairs rather than exhaustively processing all possible combinations. The method identifies sufficient correction information from a subset of correlations, achieving adequate precision without the excessive computational burden of complete volumetric self-calibration
Data Source
AI summary
A method calibrates an optical measurement set-up with a measurement volume seeded with particles and at least two cameras so that the measurement volume can be mapped from different observation angles. The method includes simultaneously mapping the measurement volume by the cameras to produce images; rectifying each camera image in relation to a common reference plane in the measurement volume by using the respective pre-calibrated mapping function; performing two-dimensional correlation for at least one pair of rectified camera images to produce correlation fields that present an elongate correlation maxima band for each correlation field; reducing the correlation maxima band to a straight line representing the band; determining the distance of this representative straight line from the coordinate origin of the correlation field as a correction value, using the determined correction values to correct the mapping functions of those cameras for which rectified camera images were included in the correlations.