Estimation of Tree Centroids Based On Terrestrial Laser Scan Data

Timber harvesting is one of the most dangerous activities in forest management, resulting in a significant number of fatal accidents every year. One of the main causes of such accidents is the incorrect determination of the felling direction and inclination of the tree. A precise forecast of the felling direction makes it possible to fell a tree in a controlled manner to avoid damage to residual stand and natural regeneration and to prevent accidents. Accurate estimation of the inclination of a tree requires skilled knowledge of tree anatomy and experience, but human error and misjudgment can never be completely eliminated. Innovative technologies as for example laser scanning can be used to provide additional support for timber harvesting planning and to minimize the risk of misjudgment. The use of Terrestrial Laser Scans (TLS) is very well suited for the detailed visualization of scanned trees. In our case, several stationary scanning processes were carried out for each individual tree resulting in individual point clouds, which represent a digital twin of the trees. Quantitative structural models (QSM) are often used to accurately estimate the biomass or volume. A very reliable way of calculating structural models from individual trees is "TreeQSM", an algorithm that is integrated into the "MATLAB" operating programme. The algorithm re-constructs the tree structure using adapted cylinders that correspond to the diameters of the individual tree segments. The statistical programming language R can then be used to query the coordinates and radii of the individual cylinders. The start and end coordinates of the cylinders are averaged in order to determine the centers of the cylinders which are used to calculate the lever arm distances. Since the dimensions of each cylinder are known, the volumes can be computed. This allows the calculation of the weight of each individual cylinder, taking the relative density into account. These numbers can then be used to derive the actual position of the tree centroid using the sum of the singular cylinder resultants. The new developed method makes it possible to determine the inclination of a tree very precisely and the force required to fell the tree in a certain direction can be derived from this. The choice of felling direction influences the productivity of timber harvesting and has an impact on the remaining stand. Therefore, a careful planning of the felling layout with the appropriate felling direction is essential to ensure the cost efficiency and working safety of timber harvesting. In order to test the practicality of this approach, the results of the calculations are compared with the estimations of forestry workers.