A Calibration and 3-D Measurement Method for an Active Vision System With Symmetric Yawing Cameras

In this study, we propose a 3-D measurement method for an active stereo vision system with two symmetric yawing cameras. First, we establish a measurement model with five constant systematic parameters and five variables. Second, we present a design for a relatively simple and convenient calibration method to determine the constant systematic parameters for the active vision system. In our proposed method, the initial yaw angles of two cameras are calibrated with a minimum of three equal interval points in a common field of view (FOV). The initial pitch angles are calibrated with at least one point in this common FOV. The initial yaw angles are used in the following calibration processes of the baseline length and the optical offset. The baseline length is calibrated with respect to two such points with known horizontal distance. An offset used to compensate for the difference between the actual optical centers of the two cameras along their optical axes is also computed with at least one feature point with the cameras yawed at different angles. Third, an associated measurement method for objects in the common FOV is presented. The proposed method computes 3-D positions of feature points in the common FOV using these five constant systematic parameters and five variables. This active stereo vision system design does not require repeated calibration for varying yaw of the two cameras to conduct measurements once the five constant systematic parameters have been calibrated offline. We conduct comparative experiments, and the results verify the effectiveness of the proposed method.