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结合中国嫦娥三号月球车探测的科学应用目标,提出了一种基于投影变换的机械臂探测点定位方法.该方法在总结鱼眼镜头成像模型基础上,建立球面投影与透视投影间的转换关系,求得球面投影中像主点坐标和球半径,利用相关参数将球面投影图像转化为透视投影图像;结合月球车上鱼眼相机的安装位置相对固定,将转换后的透视投影图像重采样生成核线影像.利用相关系数和最小二乘匹配,在鱼眼相机核线影像上实现特征点的亚像素级匹配.通过前方交会计算探测点的三维坐标,并结合探测点邻域点坐标拟合最佳空间平面,获取平面的法向量,即机械臂探测点的定位.采用该方法对仿真图像进行了定位计算,并将计算值与仿真真值进行比较,总误差约为2 mm.实验结果表明,该方法完全能够满足嫦娥三号月球车机械臂探测的定位精度.
Combining with the scientific application of Lunar rover exploration in Chang’e III, this paper proposes a method of locating the detection point of the robotic arm based on projective transformation.The method builds the transformation relationship between the spherical projection and the perspective projection based on the imaging model of the fisheye lens , The coordinates of the main point and the radius of the sphere in the spherical projection are obtained, and the spherical projection image is transformed into the perspective projection image by using the relevant parameters. The installation of the fisheye camera on the lunar rover is relatively fixed, and the converted perspective projection image is resampled Nuclear line image.Using the correlation coefficient and least squares matching, sub-pixel level matching of feature points is realized on the fisheye camera’s line image.Firstly, the three-dimensional coordinates of the probe points are calculated and fitted with the coordinates of the neighborhood points of the probe points The best space plane is obtained and the normal vector of the plane is obtained, that is, the location of the detection point of the robot arm.Using this method, the simulation image is located and compared with the simulation true value, the total error is about 2 mm. It shows that this method can fully meet the positioning accuracy of the Lunar III lunar rover.