Accurate calibration method for a range finder based on a 3-D model of the optical system

Range finding based on the projected light method is superior as a highly reliable means of obtaining dense three-dimensional (3-D) information about scenes. The use of this method, however, demands the development of an accurate calibration method. This paper proposes a method in which the optical system of the range finder is divided into the region surrounding the video camera and the region surrounding the light sources and rotational mirror, and calibration is by the method of least squares. The optical system is modeled in three dimensions and includes geometrical parameters not taken into account in earlier methods such as the torsion of the rotational axis of the mirror. Therefore, this method can be used with the camera and the light source located in any positions. In addition, only a calibration board with a reference pattern is used as a jig. Therefore, highly reliable results are obtained easily because no components other than those of the range finder intervene. This calibration method was applied to the multilight-sources range finder developed by the authors to evaluate its accuracy and to verify its validity.