中文摘要：

【目的】将使用三维激光扫描仪获取的树木点云构建树木三维模型与提取树木参数相结合,构建适用于树干参数提取的树干三维表面模型。【方法】采用三维表面重建技术,根据树干点云特征改进基于切平面投影的表面重建算法,并将其应用于重建树干的不规则三角网表面模型中。改进内容如下：1）使用半径阈值作为邻域点的选取准则以减少点云分布散乱对邻域点集选择的影响;2）根据点之间距离越近、影响越大的思想,使用距离加权方式计算特定点处切平面的法向量,且当邻域点集投影至切平面上产生重复投影点时,删除距离较远的邻域点;3）根据点集在平行平面间投影的几何拓扑不变性简化投影切平面的构建;4）以点集旋转方式简化三维平面点集到二维平面点集的转换。本研究提出的改进算法将当前点及其邻域点集投影至切平面上得到一个平面点集,将平面点集上构建的Delaunay三角网的连接关系映射到树干点云中以构建当前点与其邻域点的三维表面模型,逐个对树干点云中的点投影重建以实现树干点云整体的三维表面重建。【结果】对杨树树干的重建试验表明,改进算法能更好地构建树干的表面模型;对粗糙程度不同的多个树种的试验表明,重建的树干表面能清晰地显示外业扫描时标注的色彩信息,局部的表面三角形面片能清晰地反映树干表面凸凹不平的特征及树干表面在三角面片处的朝向信息;从重建表面上提取直径的试验表明,与围尺实测直径相比,从重建表面上提取直径的RMSE为0.18 cm,验证了重建树干表面的精确性。【结论】本研究从参数提取角度,采用表面重建方法,改进了基于切平面投影重建算法以重建树干的三维不规则三角网表面,重建的树干表面具有较好的视觉效果,能真实反映树干表面的特征。本研究提出的改进算法适用于构建逼真?

英文摘要：

【Objective】Three dimension（3D） tree modelling and tree parameters extraction from the three dimensional laser scanning data are the two research focuses in recent years. Combining the two contents,the objective of this study is to reconstruct the irregular triangulation surface of the stem that can be used for extracting stem parameters. 【Method】The technology of three dimensional surface reconstruction was used in this study. The algorithm of surface reconstruction which based on tangent plane projection in the three dimensional spaces was improved according to the characteristics of stem point cloud. And the improved algorithm was applied to reconstruct the irregular triangulation as the stem surface model. The improvement was as follows： 1） Radius value was chosen as the criterion for choosing nearest neighbor point set to reduce the influence of the scattered distribution of stem points; 2） The closer the distance between points,the greater the impact between points,the tangent normal vector of a point was calculated by the weighted distance method. And the farther neighbor point was deleted when there are the same project points in the tangent plane of the neighbor point set; 3）According to the geometric topological invariance of the project point in the parallel plane,the calculation of tangent planewas simplified; 4） The transforming of planar point set in the three dimensional spaces to planar point set in the two dimensional spaces was simplified by point set rotating. In the improved algorithm,the current point and its’ neighbor point set were projected to the tangent plane and a planar point set was generated. The connected relationship in the Delaunay triangulation of the planar point set was mapped into the stem point. Then,the surface model of the current point and its neighbor points was reconstructed. The global stem surface was obtained through the above reconstruction procedures one point by one point. 【Result】The reconstruction experiment of Populus sp. stem showed t