Research on positioning method of digital zenith camera under rough leveling state

A positioning method of digital zenith camera was proposed to solve the problem that the traditional positioning method required precise leveling of the instrument, the data fitting model parameter was inaccurate and the positioning iterative process was complicated. The calculation formula of CCD image coordinates in the horizontal state was derived. CCD image coordinates of the horizontal state were obtained by using the CCD image coordinates under rough leveling and the output value of the inclinometer, and the star tangent plane coordinates under rough leveling were analyzed, the analysis results showed that the star tangent plane coordinates which needn't be correct could be used to establish data fitting model. The parameters of the data fitting model were calculated by the robust estimation, which restrained the influence of rough error on the parameters and improved the accuracy of the data fitting model. In the end, positioning iterative process was optimized by solving the simultaneous equations of data fitting model to gain the CCD image coordinates of rotating axis, eliminating the inverse transformation of data fitting model and taking the average of the plane coordinates, which improved the efficiency and ensured the positioning accuracy. The experimental results showed that the positioning precision of positioning method under rough leveling is basically the same as the positioning method under fine leveling state. The accuracy of the positioning longitude under rough leveling is 0.306, the accuracy of the latitude is 0.292. Positioning accuracy satisfies the positioning requirement of digital zenith camera.