Iteration of B-spline surface based deflectometric method for discontinuous specular surface

There is an over-growing demand for accurate three-dimension model of industrial components. In the measurement of specular surface, deflectometry has been widely used for its convenience and high accuracy. However, it is a challenge to measure discontinuous specular surface by the traditional deflectometry. In order to solve this problem, this paper proposes a deflectometric method based on iteration of control points of B-spline surface. In this method, a screen at two positions displays fringe patterns which will be reflected by specular surface under test and captured by a camera. According to the undistorted and absolute unwrapped phase map, a continuous zone containing all discontinuous area which is distinguished by a direct deflectometric method, is fitted by a B-spline surface with an estimated depth on the focus plane of the camera. Meanwhile, empty points and basis functions bridging isolated surface are removed. The control points of the fitted surface are solved by iterative calculation. With the solved control points, discontinuous specular surface is reconstructed. Simulated and actual experiments are carried out and the results show high accuracy and stability of the proposed method.