基于二维成像的球心坐标高精度定位方法

High Accuracy Positioning Method Based on 2DImaging for the Coordinates of the Center of a Sphere

球体由于其旋转对称性和成像不变性,在双目视觉系统中作为球型靶标具有独特优势。然而球体在像面的成像一般是椭圆,而不是标准圆,其椭圆中心与球心成像点并不是同一个点,这就会对球心的空间定位带来误差。为了找到真实的球心成像点坐标以提高球心的定位精度,建立并分析了空间球的成像模型。基于针孔成像模型和透视成像原理,提出了一种球心成像点的高精度定位方法。该方法结合相机焦距,对边缘点进行畸变校正后可直接拟合出球心成像点坐标。仿真分析了边缘噪声以及边缘提取不完整对所提方法的影响。最后通过实验验证了所提方法可以显著提高球心坐标的定位精度,适用于双目视觉中球靶标的定位以及其他需要对球心进行定位的应用中。

Owing to its rotational symmetry and imaging invariance,a sphere has unique advantages when used as a spherical target in binocular vision systems.However,the image of a sphere on an image surface is generally an ellipse,rather than a standard circle,and the center of the ellipse does not coincide with the center of the sphere,resulting in errors when the location of the sphere′s center is determined.To calculate accurate image coordinates of the center of a sphere to improve positioning accuracy,imaging models of spheres in space are established and analyzed,and a high-precision positioning method for the image of a sphere′s center is presented based on the pinhole imaging model and perspective imaging principle.Combined with the focal length of the camera,the image coordinates of a sphere′s center can be calculated after distortion correction of the edge points.The influence of edge noise and incomplete edge on this method is simulated and analyzed herein.Finally,the experimental results show that the proposed method can significantly improve the positioning accuracy of an image of a sphere′s center;therefore,the proposed method is suitable for the positioning of a spherical target in a binocular vision system and for other applications requiring the accurate positioning of the center of a sphere.