Study on flexible calibration method for binocular stereo vision system

Abstract

Using a binocular stereo vision system for 3D coordinate measurement, system calibration is an important factor for measurement precision. In this paper we present a flexible calibration method for binocular stereo system calibration to estimate the intrinsic and extrinsic parameters of each camera and the exterior orientation of the turntable's axis which is installed in front of the binocular stereo vision system to increase the system measurement range. Using a new flexible planar pattern with four big circles and an array of small circles as reference points for calibration, binocular stereo calibration is realized with Zhang Plane-based calibration method without specialized knowledge of 3D geometry. By putting a standard ball in front of the binocular stereo vision system, a sequence pictures is taken at the same by both camera with a few different rotation angles of the turntable. With the method of space intersection of two straight lines, the reference points, the ball center at each turntable rotation angles, for axis calibration are figured out. Because of the rotation of the turntable, the trace of ball is a circle, whose center is on the turntable's axis. All ball centers rotated are in a plane perpendicular to the axis. The exterior orientation of the turntable axis is calibrated according to the calibration model. The measurement on a column bearing is performed in the experiment, with the final measurement precision better than 0.02mm.