基于三维点云的苹果树叶片三维重建研究

Apple Tree Leaf Three-dimensional Reconstruction Based on Point Cloud

摘要:

叶片是果树冠层的重要组成部分，对其进行三维重建研究不仅可以对叶片形态特征进行分析，还能为冠层光照分布计算以及果树整形修剪提供理论基础。三维激光扫描仪以非接触、高效、快速获取数据的优势被大量应用于三维空间信息采集工作中。本文提出一种基于三维点云的苹果树叶片结构形态三维重建方法。首先针对叶片的形态特点选择合适的三维激光扫描仪获取苹果叶片三维点云；基于包围盒法搜索K邻域，计算点云中点与其邻域点的平均距离，并设定距离阈值作为判定中心点是否为离散点的依据，进而确定离散点并去除；利用最小二乘原理实现点云局部曲面拟合以及法向量、曲率的计算，提取叶片边界点；对于非边界点部分，根据中心点法向量与其邻域法向量的关系，对点进行不同程度的精简；最后对处理后的叶片点云完成三维重建。结果表明，构建的叶片模型能够较好的保留叶片的三维形态特征，可以为果树冠层重建和光照分布计算提供基础。

关键词:苹果叶片;三维重建;点云去噪;点云精简;曲率计算

Abstract:

The canopy leaf is an important part for the fruit tree development, and the spatial distribution and morphological structure of canopy plays a vital role in fruit yield and quality. The study on three-dimensional (3D) reconstruction of apple tree leaf blade can not only analyze the morphological characteristics, but also provide the theoretical basis for the calculation of canopy light distribution and pruning of fruit trees. With the rapid development of laser scanner technology, three-dimensional laser scanner is widely used in 3D reconstruction of different fields due to the advantages of non contact, high precision and high efficiency. A method was proposed for 3D reconstruction of apple tree leaf blade based on point cloud. And the accomplishment of the 3D reconstruction method was on the basic of presented point cloud simplification method. First of all, 3D laser scanner was used to obtain point cloud of apple tree leaf blade. Secondly, search the K-neighborhood points based on the bounding box method and calculate the average distance between the midpoint and its neighbors. The noises were identified according to distance threshold and then they were removed . Thirdly, extract the boundary feature points and retain them as a mandatory feature area. For the non-boundary points, according to the relationship between the midpoint normal vector and its neighbor normal vector, the points were reduced to different degrees. Finally, the 3D reconstruction of apple tree leaf blade is realized. The results showed that the constructed leaf model can preserve the 3D morphological features of the leaf, which can provide a basis for further canopy reconstruction and light distribution calculation.

Key words:apple tree leaf;three-dimensional reconstruction;point cloud de-noise;point cloud simplification;curvature calculation