Proposal for the Development of a 3D Hybrid Model for the Hellenic Cadastre

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Cadastral registration based on a two-dimensional parcel representation of space (2D cadastral unit) was adequate for several decades. However there has been an active and increasing use of space above and below the land surface with a fragmented legal status (various properties, property rights, right-holders). Thus, encouraged by the recent technological developments the use of three-dimensional approaches in cadastral systems (3D-cadastral unit) is investigated. The spatial databases, 3D GIS and CAD applications can be effectively used for 3D modeling, spatial analysis and visualization of cadastral objects. Greece has rural areas of intense relief with various autonomous properties at various levels (parcels, single family houses, mines etc), with overlapping property projections in a 2D-unit system. In the highly urbanized areas, too, there are autonomous properties like condominiums, metro, motorways, utility networks, etc, which have overlapping projections in a 2D-unit system. The technical specifications of the Hellenic cadastre (HC) require the creation of a 2D-unit cadastral GIS; there are no provisions for a 3D-cadastral unit reference for the legal rights and the other cadastral information. This paper proposes a smooth transition from the existing HC 2D-GIS to a 3D hybrid model, so as to preserve the existing 2D-unit system but also integrate 3D representations of the physical objects. An application of a 3D cadastral process is developed for the island of Kimolos, in which typical examples of special real property objects exist, such as settlements carved into the rocks with overlapping projections of the private properties, and/or settlements with buildings arching over the alleys with overlapping projections of the private and public properties. Aerial and terrestrial images of the island of Kimolos, and the existing cadastral map are combined with the descriptive information of the cadastral records and entered into the spatial database system. The development of the three-dimensional cadastral system is approached by three different methods. In the first two methods the cadastral registration of objects is implemented in the SDBMS of Oracle Spatial, which is linked to a Geographic Information System (ArcInfo) and AutoCAD Map 3D, respectively, so that the properties are visualized in three-dimensional level. In the third method, the registration and 3D representation of cadastral objects are implemented in the environment of ArcGIS, while for their 3D modelling Google SketchUP is chosen, because of its capability to incorporate 3D models to ArcGIS.