Dynamic calibration of stereo photogrammetric system based on optical reference bar

A new method for calibrating stereo photogrammetric system is presented. The relative position of the two cameras are determined from epipolar constraint and computed through linear normalization eight-point algorithm and M-estimator method. Calibration is carried out by moving a scale bar, which has six small infrared LED marks and the distances between these marks have been certified, in a pattern in and around the measurement volume. The distances between these marks are used to determine the scale factor and the cross ratio invariant of the two distances between the three marks on rigid reference bar is used to verify the matching quality. Due to take infrared LED as feature point and the light intensity of these feature points can be automatically controlled according to the distance between cameras and reference bar, the imaging feature points have uniform intensity profile and high contrast with background, and hence the calibration accuracy is improved. The simulations and experimentations have shown that the calibration accuracy can be compared with complex off-line calibration.