Extraction of structure elements in laser scanner data

Currently laser scanning is being pushed by developments and innovations from the producers and vendors of the scanners, this statement is valid for airborne laser scanning (ALS) as well as for terrestrial laser scanning (TLS). The research and development on the restitution of laser scanner data, on the other hand, lag behind. The difference is most notable in the area of TLS. Within this applied project a substantial contribution to this subject - for ALS as well as TLS - shall be made. A large improvement in the quality of the restitution methods can be achieved, if so-called structure elements can be extracted automatically from the laser scanner data. Due to the high quality niveau, the methods to be found must operate on the original data and must be desined for the 3D-space. In the course of the applied project the following subjects shall be treated: +) Extraction of structure elements, especially break lines in 3D point clouds, and modelling of the terrain with the original ALS-data and the extracted structure elements. +) Rigorous adjustment of the ALS-strips, especially under consideration of the structure elements in the overlapping zones of the strips. +) Simultaneous transformation of free stationings from TLS in a superior (building) co-ordinate system. +) Modelling of buildings from the original TLS data together with the extracted structure elements as CAD- models. The terrain models, which could be derived with the new methods from the ALS-data, would - on the one hand - have a very high geomorphological quality, and - on the other hand - fulfill the high demands of hydrologists for flood simulations. Dams which shall be modelled with break lines, are - as generally known - the flood inhibitors. CAD models, which could be derived with the new methods from the TLS-data, would be a good basis for computer aided facility management which gains more and more importance. This is applicable for historically valuable buildings as well as complex new buildings.

Laserscanning, also often referred as LiDAR (Light Detection and Ranging), has revolutionised the area of topographic surveying as well as close range object acquisition in the last years. This trend was manly pushed by developments and innovations from the producers and vendors of the scanners allowing a very dense and highly automated object acquisition. In contrast, the research and development on the restitution of laser scanner data lag behind. Therefore, the focus of this research project was the development of adequate methods in order to utilise the acquired information. A large improvement in the quality of the restitution methods can be achieved, if so-called structure elements are extracted from the laser scanner data. Therefore, the main issue of this project was the automated extraction of structure elements (especially breaklines) in 3D point clouds. For this task a basic modelling concept, that allows the formulation of 3D breaklines from laser scanner data but also from any kind of point cloud data, was developed. For the use in practice a high degree of automation within this process is essential. In order to reach a high quality level, the methods have to operate on the original measured randomly distributed point cloud data and must be designed for 3D space. Next to this main theme, the other research issues of the project regarded the tasks of adjustment of laser data, data quality, automated feature extraction, digital surface modelling using structure information, and data reduction. The terrain models derived with these new methods have a very high geomorphologic quality and fulfil the high demands of the hydrologists for flood simulations. Especially dams, which are - as generally known - the flood inhibitors, can be modelled accurately with the help of the developed algorithms. Furthermore, in the close range object acquisition the determined structure lines lead to CAD models, which can be a good basis for the computer aided facility management, which gains more and more importance. This is applicable for historically valuable buildings as well as for complex new ones.