Roads and buildings from laser scanner data within a forest enterprise

Laser scanning with its ability to penetrate vegetation and its extremely high point density allows for a completely new approach to semi-automatically delineate man-made features (“objects”) in forested areas as a basis for the management of such data in a GIS. In this paper, emphasis is laid on the detection of roads and buildings from laser scanning data. The basis of our analysis is the generation of a DTM actually representing the earth surface (no tree tops, no building roofs). From a slope model of the terrain, break lines can be detected by applying standard edge extraction techniques. However, the slope model is still too noisy to deliver “good” (long, continuous) break lines. Thus, a pre-processing step making use of an edge-enhancing filter becomes necessary. From the results of break line detection, a new, geomorphologically revised terrain model can be derived. The break lines contain the road edges which can be interactively selected by the user. With respect to roads, the line extraction results can be improved using a snake algorithm. Building candidate regions can be detected from the differences of surface models derived from the original “last-pulse” and “first-pulse” laser data and the rectified ground model. The algorithm is based on a classification of elevation difference models followed by the improvement of classification results by a despeckle filter, the main problem being the distinction of tree tops from buildings. In this paper the algorithms involved for the solution of the above tasks are described and first test results are presented.