Describing Forest Stands Using Terrestrial Laser-scanning

A method for extracting forest parameters is described in this paper. The 3D point clouds derived from phase difference laser scanners in forests were processed in a step-wise separation. The first step contains basic filter methods to reduce raw data which, separates isolated points or deletes those artefacts resulting from the ambiguity problem. The next step includes using algorithms to isolate the main object categories of forest stands: terrain and trees. A digital terrain model (DTM) is calculated as a triangulated irregular network (TIN). Based on this, the point clouds are sliced at different heights above ground and included co-ordinates are projected in 2D layers. The following steps use image analysis methods to derive the single tree positions and diameters in the different layers. A Hough-transformation is used for the detection of the trees and a circle approximation is used to localise the tree exactly. For a precise model of a tree stem, a triangulation is conducted using the power crust algorithm. The developed methods enable one to measure some of the standard forest inventory parameters. Unfortunately, important parameters such as tree species and tree height have not yet been extracted from the scanning data. Indeed, for the acceptance as a standard method, these parameters play a key role. Further work has to investigate an automatic way to extract these parameters from the point cloud. * Corresponding author.