A 3D Virtual Model of the Gorizia Downtown (Italy) by Matching Aerial and Terrestrial Surveying Techniques

This paper deals with the various aspects of the Gorizia downtown (Italy) 3D virtual model production obtained by a suitable integration of laser and imaging data, both acquired either by means of a helicopter and a terrestrial surveying. An aerial high-density (15 points/m2) laser surveying was achieved with an Optech ALTM 3033 system for an area of almost one square kilometre. High-resolution Rollei DB44 digital images were also acquired for the same area. The filtering, classification and 3D building modelling have been successfully carried out by the well-known TerraScan software(Terrasolid); moreover, the highresolution true orthophoto (0,2 m/pixel) has been accomplished by means of TerraPhoto (Terrasolid). To fulfil a photo-realistic 3D city model, the aerial orthophoto has been mapped onto the DTM and the building roofs. Nevertheless, to truthfully represent also the building façades of some streets and squares, even a terrestrial survey was carried out. Laser scanning was done by Riegl LMS Z360i system, and a simultaneous acquisition of digital images by “on system” Nikon D100 was carried out. Thanks to reflecting targets set on the facades, topographically measured and automatically detected, the different terrestrial models have been registered and geo-referenced in the same datum (Gauss-Boaga Italian cartographic frame) of the aerial laser surveying. Finally, the paper shows the aerial and terrestrial orthophotos wrapped on the different surfaces and the extremely faithful 3D visualization of the city so reached. This permits fine virtual navigation also for terrestrial trajectories and not only for aerial ones to enjoy in VRML interactive environment or in AVI movies for tours above and around the streets of Gorizia.