Light-field cameras are gaining attention for their unique light gathering and post-capture processing capabilities. In our previous work, we combined light-field imaging with structured light technology to realize three-dimensional (3D) reconstruction for highly reflective surface. However, due to the lack of effective calibration of the light-field camera and reconstruction systems, it cannot meet the requirements of precise 3D measurement. A universal sub-aperture image extraction algorithm for the light-field camera with hexagonal microlens is presented to accurately extract the multidirectional images. Then, we explore the spatial relationship in equivalent camera array (ECA) of focused light-field camera according to the perspective variation of sub-aperture images. After that, an accurate 3D measurement system based on ECA model is proposed to achieve 3D measurement for highly reflective surface. To test the system’s practical performance, a precision analysis is conducted for a standard gauge block with ground truth. By comparing the reconstruction result of traditional method and ours, we demonstrated the validity of the proposed method to perform 3D measurement for highly reflective surface.
KEYWORDS: Distance measurement, Cameras, Laser systems engineering, Prisms, Monte Carlo methods, Manufacturing, Laser applications, Imaging systems, 3D modeling
The Six-degree-of-freedom(6-DOF) measurement system based on laser tracking equipment provides a good solution for large-scale industrial measurement. However, there is no unified standard to evaluate the accuracy of attitude measurement system. At present, the accuracy evaluation method of attitude measurement mainly adopts the comparison method of standard parts, which is easily constrained by space dimensions. Aiming at this problems, a homogeneous coordinate transformation method based on spatial distance constraint is proposed to realize the on-site accuracy evaluation of attitude measurement. Firstly, a reasonable control field was arranged, and the distance constraints between the reference points and the measuring points were established. Secondly, the mathematical model which described the relationship between space distance and attitude was established by using homogeneous coordinate transformation matrix. Through the above evaluation method, the accuracy of attitude measurement can be evaluated by tracing the measurement results of attitude angle to the length measuring standards. The simulation results show that the accuracy of the evaluation model decreases linearly with the measurement distance of attitude measurement system. Assuming that the measurement accuracy of the distance constraint is 15μm+6μm/m, the size of the control field is 1.1m*6.4m*5.6m, and the attitude angle range is [-60°, 60°]. The accuracy of the evaluation model can be controlled within [0.34°,3.25°], when the working distance is 3 to 15 meters. This method provide an effective idea for the on-site evaluation of attitude measurement accuracy.
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