Methods for the three-dimensional (3D) reconstruction of forest trees have been suggested for data from active and passive sensors. Laser scanner technologies have become popular in the last few years, despite their high costs. Since the improvements in photogrammetric algorithms (e.g. structure from motion—SfM), photographs have become a new low-cost source of 3D point clouds. In this study, we use images captured by a smartphone camera to calculate dense point clouds of a forest plot using SfM. Eighteen point clouds were produced by changing the densification parameters (Image scale, Point density, Minimum number of matches) in order to investigate their influence on the quality of the point clouds produced. In order to estimate diameter at breast height (d.b.h.) and stem volumes, we developed an automatic method that extracts the stems from the point cloud and then models them with cylinders. The results show that Image scale is the most influential parameter in terms of identifying and extracting trees from the point clouds. The best performance with cylinder modelling from point clouds compared to field data had an RMSE of 1.9 cm and 0.094 m³, for d.b.h. and volume, respectively. Thus, for forest management and planning purposes, it is possible to use our photogrammetric and modelling methods to measure d.b.h., stem volume and possibly other forest inventory metrics, rapidly and without felling trees. The proposed methodology significantly reduces working time in the field, using ‘non-professional’ instruments and automating estimates of dendrometric parameters.

中文翻译：

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从智能手机摄影测量点云估计树的直径和体积

对于主动和被动传感器的数据，已经提出了对森林树木进行三维（3D）重建的方法。尽管激光扫描仪技术成本高昂，但在最近几年已变得越来越流行。由于摄影测量算法（例如，运动SfM的结构）的改进，照片已成为3D点云的新型低成本来源。在这项研究中，我们使用智能手机相机捕获的图像来使用SfM计算森林图的密集点云。通过更改致密化参数（图像比例，点密度，最小匹配数）来生成18个点云，以研究它们对所产生的点云质量的影响。为了估算乳房高度（dbh）和茎干处的直径，我们开发了一种自动方法，该方法可以从点云中提取词根，然后使用圆柱体对其进行建模。结果表明，就识别和提取点云中的树木而言，图像比例是最有影响力的参数。与现场数据相比，从点云进行圆柱建模的最佳性能是RMS值为1.9 cm和0.094 m³，分别用于dbh和volume。因此，出于森林管理和规划目的，可以使用我们的摄影测量和建模方法来快速，不砍伐树木的情况下测量dbh，茎量和其他森林清查指标。拟议的方法使用“非专业”仪器并自动估算树突参数，可显着减少现场工作时间。