In the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) project, the fiber should precisely align with the celestial target to obtain the spectrum of the star, and the position accuracy of the fiber in the focal plane directly affects the spectral quality. LAMOST uses photogrammetry to acquire the actual position of the fiber. However, the fiber view camera system without precise internal control points in the focal plane negatively affects measurement precision. To solve this problem, we propose a fiber position measurement method based on the external planar target (EPT) that replaces the internal control points with the external control points; multiview reconstruction and bundle adjustment with additional position constraints are used to calculate the position of the fibers. The validity of the measurement method is verified by the simulation and experiment. The preliminary results show that the method has good stability and the measurement accuracy of the fibers can reach 20 μm. Because the external control points are distributed on the EPT plane, the assembly error of the EPT and focal plane does not affect the measurement accuracy. Therefore, the proposed method can achieve precision measurement under nonprecision installation conditions.
The positional accuracy of a near-infrared (NIR) dynamic navigator is remarkably affected by two factors. One is the calibration accuracy of the navigator’s two NIR cameras, and the other is the accuracy of feature point extraction. The current lack of accurate calibration devices for NIR cameras limits further application. Therefore, in this study, an NIR camera calibration device was designed by placing the NIR light source and heat dissipation system at the back of a Halcon transparent glass template. Usage of camera calibration in a specific band and the gray centroid method based on elliptic boundary to extract feature points can further improve the accuracy of vision system calibration and measurement. Repeated tests and verifications showed that the reconstruction accuracy (<0.1 pixels) of the binocular vision system calibrated by the NIR calibration device in a specific band was better than that calibrated by traditional methods.
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