为实现深空探测中对行星目标的光学自主导航, 提出了亚像素精度的行星中心定位方法。首先, 建立了导航相机和目标行星的坐标变换关系, 结合光学成像理论分析了行星成像的边缘特性; 提出使用行星图像有且仅有的一段半圆形边缘, 通过圆拟合法实现行星的中心定位。然后, 根据行星图像的边缘分布特征, 改进了Canny算法以快速提取行星的真实边缘, 并利用最大距离法提取半圆形边缘。最后, 分析了传统高斯函数亚像素边缘检测算法的理论依据, 基于成像理论提出了改进型高斯函数亚像素边缘检测算法, 并通过圆拟合求得行星的亚像素中心。仿真和月亮实拍实验显示, 改进型定位算法的精度达到了0.02和0.68 pixel, 比传统插值算法约高0.03和0.21 pixel, 在可靠性、定位精度、抗噪声等方面均满足深空探测的需要。

To realize the autonomous optical navigation of planets in deep space exploration, a planetary center measurement method with sub-pixel accuracy was presented. Firstly, the coordinate transformation between a navigation camera and a target planet was established. According to optical imaging theory, the edge characteristics of a planetary image were analyzed. Using the only one semi-circle edge of the planetary image, planetary center was measured through circle fitting. Then, according to the edge distribution characteristics of the planetary image, the real semi-circle edge of planet was extracted by modified Canny algorithm and the longest distance method. Finally, the theory basis of traditional sub-pixel edge detection algorithm was analyzed based on Gauss fitting, improved sub-pixel edge detection algorithm based on Gauss fitting was presented according to imaging theory and the sub-pixel center of planet was obtained through circular curve fitting. In simulation experiment and moon testing experiment, the accuracies of modified algorithm are 0.02 and 0.68 pixels, which are higher about 0.03 and 0.21 pixels than that of traditional algorithm. It can satisfy the requirement of deep space exploration for reliability, positioning accuracy and noise immunity.