Airborne laser scanning can be employed today for the production of large scale maps and the creation of detailed 3D city models. For this purpose, several solutions have been proposed, also available in commercial software, to make easier and semi-automated the extraction and the geometric modeling of buildings from LIDaR data. As a consequence, while 3D urban modeling is gaining popularity among architects, engineers and urban designers, proper investigations are addressed to evaluate the likelihood and the accuracy of this new kind of survey products. In this paper, after a concise analysis of the possible errors affecting the building model construction, and a brief description of the
principal methods to achieve it, we illustrate our experience in the realization of a detailed 3D model of the city of Gorizia (NE Italy), using the TerraScan software on two different laser scan datasets taken at different sampling densities (2 points/sm and 15 points/sm, respectively). Finally, we discuss the results of a test involving one set of 25 buildings, extracted from the city model and
topographically surveyed by reflectorless EDMs and GPS equipment, in order to establish their effective size and shape. The comparison between the models obtained from the LIDaR and the real ones from the conventional survey outline that the likelihood and accuracy of the models derived from a 15 points/sm laser surveys are equivalent to those obtained by topographic measures.
