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The process of rendering and interacting with large scenes in web systems is still an open problem in 3D urban environments. In this paper we propose a prototype to visualize a city model in a client-server architecture using open-source technologies like WebGL and X3DOM. Moreover, free navigation around the scene is allowed and users are able to obtain additional information when interacting with buildings and street furniture. To achieve this objective, a MySQL geodatabase has been designed to store both geometric and non-geometric urban information. Therefore, the extra data about the urban elements is obtained through queries in the database. The communication process between MySQL and the X3D model is performed by Ajax.

Visibility determination is an essential topic in computer graphics when visualizing large scenes. This problem can be addressed using many different techniques, but most of them discard obtaining an exact visible set because it is more time consuming compared with the solution provided by the graphics hardware. However the problem remains if the scenes must be visualized in a mobile device and the visible scene must be transmitted via the Internet. In this paper we introduce a new approach based on ray shooting for obtaining an exact visibility set in polygonal scenes in R 2 and prism-shaped objects in R 3 . In both cases the scene is divided into disjoint regions using the polar diagram, a plane partition based on angle preprocessing. The polar diagram allows to improve computation times while ensuring accurate results in these scenes.