Ortega, Maria Dolores RoblesCoelho, AntónioSousa, A. AugustoAlvarado, Lídia OrtegaCoelho, António and Cláudio, Ana Paula2021-06-182021-06-182021978-3-03868-154-0https://doi.org/10.2312/pt.20091244https://diglib.eg.org:443/handle/10.2312/pt20091244Most of the urban models nowadays consider towns as a flat area without sloping zones. However, in order to obtain a realistic model of a city we need to include the information provided by its Digital Elevation Model (DEM). A global representation using the surface topography and the if1:formation usually given by an urban GIS (the geometry o,f buildings, blocks and streets and additional data about street names, number of floors in buildings, etc.) could provide realistic 3D models of urban environments. Nevertheless we find many non-solved problems to deal with, which we address in this paper and provide some research directions.10.2312/pt.20091244313-314