VEGETATION MODELLING BASED ON TLS DATA FOR ROUGHNESS COEFFICIENT ESTIMATION IN RIVER VALLEY

Many environmental studies such as generation of hydrodynamic models, that are tools for risk management, require information about vegetation conditions. The description of vegetation from the hydraulic modelling point of view should include type, distribution and arrangement of existing plants. Geometric parameters of plants can be determined on the basis of laser scanning data. Terrestrial laser scanning (TLS) allows to determine precisely not only the external shape of the plant, but the geometry of individual branches as well. A method for macro and micro-structure estimation of a single shrub is presented in this paper. The data used in the research were measured with Leica ScanStation II. In the macro-structural approach, where the plant is considered as a compact solid, it is important to choose those measurement points that represent the surfaces of the plant. To achieve better matching to the non-convex parts of the hull the use of a multi-stage solid generation procedure is proposed. In this approach points are divided into segments with common edges. The method assumes that the plant is divided along the z axis into segments of a given width. First, points from one segment are projected onto the division plane. Then, 2D convex hull is generated for all the points. Finally, selected points (again in 3D space) are used for 3D convex hull generation. In order to define the geometry of vegetation the micro-structure procedure is supplemented by the segmentation algorithm to split points into groups, which form one branch. To verify the accuracy, the total surface area and the total shrub volume of branches calculated for individual variants were compared with the total surface area and volume derived from the direct measurements. Additionally, the qualitative analysis was also carried out.