Three-demensional GIS visility analysis based on urban DEM

Urban DEM (Digital elevation model) is widely used in many aspects of socialization applications, such as spatial analysis of GIS, urban planning management, visualization analysis of urban landscape, analysis of terrain visibility etc., for it can properly express the 3-dimentsional structures of modern cities. Hence, a robust, simple and accurate method for Urban DEM generation is vital. Visibility analysis has an important role in many fields of scientific research and practical applications; and much work has done in the 2-dimensional topographic analysis. However it hasn´t done much in 3-dimensional GIS analysis function. The aim of this paper is twofold: how to build up the Urban DEM and how to implement the 3D visibility analysis based on Urban DEM. In this paper we convert 1:500 scale CAD form terrain data to vector graphics, and then fusion with DEM to produce 5m resolution Urban DEM, which represents the older section of Nanjing. Our experiments results suggest the feasibility and validity of the 3D visibility analysis based on Urban DEM.