Zhenzhong Wei

A position-distortion model of ellipse centre for perspective projection

In vision inspection applications, for perspective projection there is a distortion in the position of an ellipses centre, which is inappropriate for high-precision vision inspection applications. Based on perspective projection and spatial analytical geometry, the coordinates of the spatial ellipses image centre are described and the practical image coordinates of the spatial ellipses centre are also given in detail. Later, a position-distortion model of the ellipses centre is established precisely for perspective projection. Meanwhile, a numerical simulation of the position distortion is completed, and some trends in its dependence on various geometrical parameters are identified. Finally, a practical structured-light based 3D vision system provides a validity check for the position-distortion model proposed in this paper. The work in this paper is significant for some relevant applications of machine vision.

A global calibration method for multiple vision sensors based on multiple targets

The global calibration of multiple vision sensors (MVS) has been widely studied in the last two decades. In this paper, we present a global calibration method for MVS with non-overlapping fields of view (FOVs) using multiple targets (MT). MT is constructed by fixing several targets, called sub-targets, together. The mutual coordinate transformations between sub-targets need not be known. The main procedures of the proposed method are as follows: one vision sensor is selected from MVS to establish the global coordinate frame (GCF). MT is placed in front of the vision sensors for several (at least four) times. Using the constraint that the relative positions of all sub-targets are invariant, the transformation matrix from the coordinate frame of each vision sensor to GCF can be solved. Both synthetic and real experiments are carried out and good result is obtained. The proposed method has been applied to several real measurement systems and shown to be both flexible and accurate. It can serve as an attractive alternative to existing global calibration methods.

The determination of the intrinsic and extrinsic parameters of virtual camera based on OpenGL

OpenGL is the international standard of 3D image. The 3D image generation by OpenGL is similar to the shoot by camera. This paper focuses on the application of OpenGL to computer vision, the OpenGL 3D image is regarded as virtual camera image. Firstly, the imaging mechanism of OpenGL has been analyzed in view of perspective projection transformation of computer vision camera. Then, the relationship between intrinsic and extrinsic parameters of camera and function parameters in OpenGL has been analysed, the transformation formulas have been deduced. Thereout the computer vision simulation has been realized. According to the comparison between the actual CCD camera images and virtual camera images(the parameters of actual camera are the same as virtual cameras) and the experiment results of stereo vision 3D reconstruction simulation, the effectiveness of the method with which the intrinsic and extrinsic parameters of virtual camera based on OpenGL are determined has been verified.