Two-step calibration method of the extrinsic parameters with high accuracy for a bistatic non-orthogonal shafting laser theodolite system

Abstract

Motivated by the increasing demands on the precision of 3D large-scale measurement, the extrinsic parameters calibration with high accuracy of the bistatic non-orthogonal shafting laser theodolite (N-theodolite) system is required. A two-step method is proposed to achieve the extrinsic parameters calibration with high accuracy in this paper. In the first step, by analyzing and setting the approximate emitted point during the motion of the laser axis in local space, the calculation of the initial extrinsic parameters can be simplified. In the second step, the above results are taken as the initial values of optimization, and the distances between the spatial laser points provided by PSD sensors with high accuracy in global space are used to construct the unconstrained optimal objective function. The proposed method is validated with the measurement experiment of the bistatic N-theodolite system, the average error of 3D coordinate measurement is less than 0.4 mm, and the average error of distance measurement is less than 0.3 mm within 5 m.