Measurement and calculation of crown projection area and crown volume of individual trees based on 3D laser-scanned point-cloud data

Forest inventory parameters such as crown projection area and crown volume are critical to the study of single-tree biomass and 3D green biomass. The objective of this study is to develop highly precise measurement and calculation methods for crown projection area and volume of single trees based on a terrestrial 3D laser scanning system. A total of 20 sample trees with different species (Pinus tabuliformis, Larix gmelinii, Betula platyphylla, Picea asperata, Fraxinus mandschurica) were selected, and 3D laser scanning system was used to capture the initial point-cloud data of all of the sample trees. A series of processing including point-cloud registration, denoising, and extraction was carried out to obtain the final point-cloud data of single trees. Finally, the proposed improved convex hull algorithms were used to calculate the crown projection area and crown volume of the single trees and compared with the results obtained by the traditional method and the geometrical simulation method. The results indicated that traditional measurement had significant fluctuation compared with the other two methods due to human-induced factors during measurement. The crown projection area (or crown volume) obtained by different methods was strongly correlated, especially for the geometric simulation and improved convex hull algorithms. With regard to the improved convex hull algorithms, the mean of absolute difference in the percentage of geometrical simulation-based results was 4.31% for crown projection area and 4.59% for crown volume, respectively. Meanwhile, the time consumed by the improved algorithms was significantly reduced, which took only 21% of the time required by the traditional measurement method, and 38% of the geometrical simulation method. Therefore, the proposed method can acquire the crown projection area and crown volume of a single tree effectively and quickly, which is of great significance for the application of 3D laser scanning technology in forestry practice.