Application Of Stereo Based Fringe Projection In Three Dimentional Reconstruction

The three-dimensional(3-D)shape of objects can provide many effective information,and it is widely used in many fields such as reverse engineering,aerospace,medical diagnosis,metallurgy,cultural relics protection and so on.With the development of various fields,higher accuracy is needed.How to reconstruct the shape of objects with high accuracy and efficiency has become a popular research direction.With the development of the optical technology and computer technology,the optical three-dimensional(3-D)shape measurement technology has also developed rapidly,such as fringe projection method.The fringe projection method has been widely used in many fields due to its high-precision,full-field measurement,non-contact,real-time and other advantages.In practical measurement,the traditional fringe projection method needs to perform phase-height calibration first to obtain 3-D coordinates with the relationship between absolute phase and height of the object surface.It is necessary to move the calibration board to several positions and solve the absolute phase distribution on the surface of the calibration board at this position,which is cumbersome.At the same time,the height and phase calculation error of the calibration board will have a great impact on the final experimental accuracy.This paper makes research on high-precision topography measurement by stereo based fringe projection method.The main work includes the following aspects:Firstly,fringe projection method is used to obtain the corresponding horizontal and vertical fringe images from different angles.The absolute phase distribution of the object surface is solved according to the obtained fringe images,which is used as the feature of the point to match the pixel coordinates of corresponding points from different perspectives.The relationship between the pixel coordinate system and the world coordinate system in the pinhole camera model is established.Combined with the principle of binocular stereo vision,the phase-height calibration in the traditional monocular projection grating method is avoided.Secondly,a cost function for phase matching in stereo based fringe projection method is proposed.By minimizing an optimization function determined by absolute phase,the corresponding points in left and right cameras can be accurately identified.The proposed cost function consists of two parts: one for calculating the squared difference of the absolute phase to ensure matching precision,and the other is selected to guarantee optimization convergence.The accuracy of pixel coordinates obtained by phase matching based on this method can reach sub-pixel level,which is higher than that of traditional phase matching method.In addition,a series of experiments are designed to prove the accuracy and applicability of this method.A 200mm×200mm plate was reconstructed by this method.The root mean square error of out-of-plane direction measurement was 0.006 mm.The shape of a table tennis ball with 40.00 mm diameter and a sphere with 117.40 mm diameter were also reconstructed.The relative error between the actual value and the diameter obtained by fitting spherical point cloud were 0.10% and 0.26% respectively.The shape of a cylinder and a human face with complex shape were reconstructed.Compared with the traditional projection fringe method,the accuracy of the proposed method is significantly improved.