Application of Photogrammetry with Separate Targets to the LAMOST

In order to obtain optical-fiber zero-point positions in the focal panel of the LAMOST,we present a method of high-precision photogrammetry based on separate calibration targets.First,according to the Tsai camera calibration model,we describe the principle of CCD-camera calibration,which is essentially a mapping from the coordinates of targets in image surface to the coordinates in object plane.We then describe the calculation methods of the coordinates in the image surface and object plane,using a centroid algorithm and the spherical trigonometry.Equations with calibration parameters are subsequently derived by the leastsquares fitting.We finally show the proper positioning of the calibration targets,and analyze the effective setting of targets to improve measurement accuracy of the optical-fiber positioning.Our experimental results indicate that the average value of residual CCD-camera calibration errors is 8.8μm and the standard deviation is 5.3μm.The measurement method is reliable and easy to be carried out.With a careful theoretical analysis the paper lists the reasons of why the residual errors are large in certain sense.This research will serve as a guidance to further measurement experiments.