应用虚拟像平面方法的圆柱表面单目重建

Cylindrical surface monocular reconstruction using virtual image plane method

针对圆柱表面重建问题,采用单面阵相机和线结构光构成视觉系统。该视觉系统采用虚拟像平面相机模型,通过构建虚拟像平面上的虚拟投影图像去除畸变的影响,通过虚拟像点和相机光心确定投影射线。提出该模型下相机光心的定位方法;利用两个平行平面上的结构光条的虚拟图像实现结构光的标定。利用线结构光在圆柱表面的光条为空间中一条椭圆弧的特性,首先计算出光条点在结构光平面上的坐标,由此提取出椭圆特征;再利用椭圆的短轴长为圆柱直径的特性获得圆柱的空间方程,实现圆柱定位;最后利用光心和虚拟像点在标定平面的投影点确定投影射线,计算出虚拟像点在圆柱面上的投影点坐标,构成柱面点云,并恢复出圆柱表面图像。实际实验中该视觉系统的测量精度达到双目视觉系统的水平,说明了虚拟像平面方法的有效性。

A monocular vision system with straight line structured light is proposed to address cylindrical surface reconstruction problem.The vision system uses a virtual image plane camera model. The distortion is corrected by computing the virtual projection image on a virtual image plane. The projective line of a world point is determined by its virtual image point and the camera center,which can be localized by the proposed method. The structured light is calibrated from the virtual images of two stripes on two parallel planes. In accordance with the principle that the stripe of the straight line structured light on a cylindrical surface is an ellipse arc,the projection point＇s coordinates on the light plane are firstly calculated for each feature point of stripe from the virtual image. Then the ellipse is extracted from the arc points. Secondly the cylinder＇s diameter is acquired because it equals to the length of the ellipse＇s minor axis,then the cylinder is localized in 3 D space. Finally,each projective line connected by the camera＇s optical center and the virtual image point is calculated. All intersections of the projection lines and the cylinder construct the point cloud of the cylindrical surface. Then the surface image can be reconstructed. In real experiments the accuracy of the vision system is close to that using binocular vision system.The effectiveness of the virtual image plane method is proved.