Qualification of holistic and generic camera-system calibration by fringe projection

Vision Ray Calibration provides a description of imaging properties of cameras by identification of an independent vision ray for each sensor pixel. Due to this approach, no model parameters of any cameras are determined in the non-linear optimization procedure of the calibration. Therefore, a setup of multiple cameras can be considered as one imaging system. This enables simultaneous and holistic calibration of an arbitrary number of cameras. Vision Ray Calibration utilizes Liquid Crystal Displays as calibration targets since these can provide the required continuous spatial coding of their surfaces by means of Phase Shifting Technique. However, displays employed as calibration targets exhibit some unfavorable properties such as flatness deviations of the surface. It is known that extending the Vision Ray Calibration by a polynomial parameterization of the display surface increases the calibration accuracy. This work investigates the influence of the order of polynomial terms employed for display surface parameterization. The stereoscopic Fringe Projection enables the evaluation of the calibration accuracy since Vision Ray Calibration of a stereo camera setup provides full system calibration for this technique. Our results confirm the significant improvement of calibration accuracy due to parameterization of flatness deviations of the display. Best calibration results were obtained by limiting the maximum order of polynomial terms to three. Our results indicate that terms of higher orders do not contribute true surface shape features.