回转形体点云的旋转轴线自动提取

Automatic extraction of rotation axis line from 3D scanned point cloud of rotational symmetric object

固体火箭发动机推力线的测定是航天器精密安装领域的一项关键技术,也是回转形体旋转轴线提取的一种代表性应用。针对现有相关方法存在的结果不够客观、可靠性不高且适应性欠缺等问题,提出了一种基于表面法矢约束的回转形体点云旋转轴自动提取方法。首先,计算形体点云的表面法矢,通过设置最小二乘法矢计算标准差阈值剔除非可靠点集,用以对旋转轴计算结果进行质量保证;然后,选用可靠点作为种子点,依据种子点同纬点集法矢之间的特殊关系对此点集进行筛选,并对提取的同纬点集进行平面拟合和空间圆拟合,得到旋转轴初值;最后,根据点云表面法矢与旋转轴之间的位置关系列出最小二乘平差的目标函数,通过迭代平差求解初值的改正数,从而得到最终的旋转轴提取结果。通过实验测试,利用模拟数据和实测数据对方法的准确度和精密度进行验证。实验结果显示:有效采样间隔点云的旋转轴提取结果偏斜量达到0.01°以内,横移量达到0.02mm以下,表明提出的方法正确,可以实现对回转形体点云旋转轴线的高可靠性自动提取。

Measurement of solid rocket nozzle thrust line is one of a key technique in the field of spacecraft precise installation and is a representative application of rotation axis line extraction of rotational symmetric object.Given that the existing methods have the problems such as nonobjective,poor reliability and low adaptability,an automatic solution for rotation axis extraction from 3D scanned high density of point cloud data was proposed,in which all the surface points and their normal vectors were utilized as constraints.Firstly,the normal vector of each point in point cloud was calculated and unreliable points were eliminated according to the standard deviation value of local planar fitting for normal vector calculation.Then,the initial value of rotation axis was achieved through planar and spherical fitting of reference points which had same latitude with the randomly selected reliable seed point.Finally,refinement result of rotation axis was calculated by solving theobjective function listed based on the relationship between normal vectors of each reliable point and the rotation axis.The test experiments were performed,and the accuracy and precision of the method were verified by simulated and measured data.The experimental results indicate that the deflection degree is under 0.003°and the transverse distance is under 0.02 mm,which satisfies the requirements of rotation axis extraction of rotational symmetric object.