Abstract
Crown volume is an important tree factor used in forest surveys as a prerequisite for estimating biomass and carbon stocks. This study developed a method for accurately calculating the crown volume of individual trees from vehicle-borne laser scanning (VLS) data using a concave hull by slices method. CloudCompare, an open-source three-dimensional (3D) point cloud and mesh processing software package, was used with VLS data to segment individual trees from which single tree crowns were extracted by identifying the first branch point of the tree. The slice thickness and number to be fitted to the canopy point cloud were adaptively determined based on the change rate in area with height, with the area of each slice calculated using the concave hull algorithm with portions of the crown regarded as truncated cones. The overall volume was then calculated as the sum of all sub-volumes. The proposed method was experimentally validated on 30 urban trees by comparing the crown volumes calculated using the proposed method with those calculated using five existing methods (manual measurement, 3D convex hull, 3D alpha shape, convex hull by slices, and voxel-based). The proposed method produced the smallest average crown volume. Gaps and holes in the point cloud were regarded as part of the crown by the manual measurement, 3D convex hull, and convex hull by slices method, resulting in the calculated volume being higher than the true value; the proposed method reduced this effect. These results indicate that the concave hull by slices method can more effectively calculate the crown volume of a single tree from VLS data.
Highlights
Forests are among the most valuable resources on Earth [1,2]; they comprise the earth’s ecosystem together with the atmosphere, soil, and water, playing an important role as a treasure trove of terrestrial biodiversity [3,4,5]
This study developed a new approach to calculating tree crown volume from vehicle-borne laser scanning (VLS) data producing a concave hull method for more accurately calculating crown slice area, and an adaptive slicing method based on the rate of change in area with height
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Summary
Forests are among the most valuable resources on Earth [1,2]; they comprise the earth’s ecosystem together with the atmosphere, soil, and water, playing an important role as a treasure trove of terrestrial biodiversity [3,4,5]. This study developed a new approach to calculating tree crown volume from VLS data producing a concave hull method for more accurately calculating crown slice area, and an adaptive slicing method based on the rate of change in area with height. (Figure 1c) have been used to calculate the planar areas of individual crown slices, which are divided into small blocks that are summed to produce the tree crown volume [7,31] Another commonly used geometric calculation method is the alpha shape approach [10,26,39,40,41,42,43,44], in which geometric reconstruction is performed from a discrete set of spatial points (2D or 3D), i.e., contours are extracted from a set of unordered points. ≤130 m Vertical angle 305◦ Horizontal angle 360◦ ±2 mm accuracy of measurement at a scanning distance of 25 m Vertical resolution 0.009◦ Horizontal resolution 0.009◦
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