Modelling 3D spatial objects in a geo-DBMS using a 3D primitive

Geo-DBMSs make it possible to manage large spatial datasets in databases that can be accessed by multiple users at the same time. These spatial datasets usually contain 2D data, while more and more applications depend on 3D data. Some examples are 3D cadastres [1], telecommunications [2] and town planning [3]. These applications mainly come from the ever-growing tendency of using living space multifunctional by building in the vertical direction, e.g. apartments, buildings over spanning a road, tunnels and bridges [1]. The present Geo-DBMSs do not support 3D primitives, but 3D spatial objects can be modelled by using 2D primitives such as polygons. This is possible by using 3D coordinates, which are supported by the Geo-DBMSs. In this way, several 2D polygons bound a 3D object. These 2D polygons can be stored in one record (multi-polygon) or multiple records. The absence of a real 3D primitive in the Geo-DBMSs however, results into two problems: