Three-Dimensional Topographic Information System

Research project P 14083 Three-Dimensional Topographic Information System Karl KRAUS, Helmut POTTMAN 11.10.1999 In many different fields of application exist the need of digital modelling of all features of the landscape. Such applications are Urban and Rural Planning, Development of Networks for Traffic or Telecommunication, Protection of Environment and Nature, Hydrology and Soil Preserving Farming etc. These natural and artificial three dimensional elements of the landscape are commonly labelled "topography" and for the above applications they have to be provided by a "Three Dimensional Topographic Information System". The sampling of data is usually done by the means of photogrammetry and remote sensing, by the use of laser scanners or simply by digitizing existing maps. From these data sources topographic objects have to be formed and modelled with appropriate concepts in a topographic information system. At the moment, data sampling by airborne laser scanning and by digitization of contourline maps, are of highest priority. In both cases it is necessary to use special algorithms for the creation of high quality surface models. In the proposed research project the mathematical modelling of topographic objects and the development of appropriate data structures are of central interest. Thereby, significant improvements in comparison to existing methods will be reached: that applies to the kind of data, which can be used to build an information system, as well as to the algorithms used for the interpolation of surfaces. For this purpose, it is necessary to combine the practical knowhow of the Institute of Photogrammetry and Remote Sensing with the more theoretical knowledge of the Institute of Geometry. During the work within the preceding project (P11336-ÖMA), an interdisciplinary group has been formed, consisting of Professors and PhD-Students of different departments of the TU Vienna. Mr. Dr. M. Köhl, member Ecole National Supérieur des Arts et Industries de Strasbourg, has to be included also. The members of this group already have gained a deep insight in the technical matters and problems of this project and - due to their high motivation many interesting results can be expected in the next two years.

In many different fields of application the need of digital modelling of all features of the landscape exists. Such applications are Urban and Rural Planning, Development of Networks for Traffic or Telecommunication, Protection of Environment and Nature and Hydrology etc. These natural and artificial three dimensional elements of the landscape are commonly labelled "topography" and for the above applications they have to be provided by a "Three Dimensional Topographic Information System". The sampling of data is usually done by the means of photogrammetry and remote sensing, by the use of laser scanners or simply by digitizing existing maps. From these data sources it is necessary to describe the topographic relevant information with the help of appropriate mathematic models in a topographic information system. Therefore it is necessary to develop special algorithms for the creation of high quality surface models. In the proposed research project the mathematical modelling of topographic objects and the development of appropriate data structures are of central interest. The goals of the project can be divided into the two groups 3D- triangulation and surface modelling. The intensions within the framework of the 3D-triangulation were on one hand the 3D-reconstruction of surfaces and on the other hand the extraction of topographic structure elements from triangulated data. Within the area of surface modelling the research was focused in the development of a smooth surface representation on the basis of a triangulation and in the definition of a data structure for natural and artificial objects. For the data generation the method laserscanning was of special interest. For the aims of this project, it was necessary to combine the applied scientific knowledge of the Institute of Photogrammetry and Remote Sensing with the more theoretical knowledge of the Institute of Geometry. Within the scope of this research project a knowledge based 3D-triangulation was developed, which allows to consider all information about the object. On the basis of the 3D-triangulation, methods, which allow a smooth surface modelling, were investigated (parametric patches and subdivision methods). Furthermore, methods for the automatic generation of a digital terrain model (DTM) from laser-scanner-data were developed. These methods for DTM determination (filtering and classification of the measured point cloud into terrain and off-terrain points) are already used in the commercial field of surveying. The results of this research project are published in two PhD Theses (Heitzinger and Pfeifer) and in numerous publications. A lot of knowledge from this research project can be found in a book by Prof. Kraus (Kraus, K.: "Topographische Informationssysteme").