In recent years the development of technology and the lifting of several technical limitations, has brought the third dimension to the fore. The complexity of urban environments and the strong need for land administration, intensify the need of using a three-dimensional cadastral system. Despite the progress in the field of geographic information systems and 3D modeling techniques, there is no fully digital 3D cadastre. The existing geographic information systems and the different methods of three-dimensional modeling allow for better management, visualization and dissemination of information. Nevertheless, these opportunities cannot be totally exploited because of deficiencies in standardization and interoperability in these systems. Within this context, CityGML was developed as an international standard of the Open Geospatial Consortium (OGC) for 3D city models’ representation and exchange. CityGML defines geometry and topology for city modeling, also focusing on semantic aspects of 3D city information. The scope of CityGML is to reach common terminology, also addressing the imperative need for interoperability and data integration, taking into account the number of available geographic information systems and modeling techniques. The aim of this paper is to develop an application for managing semantic information of a model generated based on procedural modeling. The model was initially implemented in CityEngine ESRI's software, and then imported to ArcGIS environment. Final goal was the original model’s semantic enrichment and then its conversion to CityGML format. Semantic information management and interoperability seemed to be feasible by the use of the 3DCities Project ESRI tools, since its database structure ensures adding semantic information to the CityEngine model and therefore automatically convert to CityGML for advanced analysis and visualization in different application areas.
Contemporary urban environment is characterized by complexity and mixed use of space, in which overlapping land parcels and different RRRs (Rights, Restrictions and Responsibilities) are frequent phenomena. Internationally, real property legislation either focuses on surface property or has introduced individual 3D real property units. The former approach merely accommodates issues related to subdivision, expropriation and transactions on part of the real property above or below surface, while the latter provides for defining and registering 3D real property units. National laws require two-dimensional real property descriptions and only a limited number of jurisdictions provide for threedimensional data presentation and recording. International awareness on 3D Cadastre may be apparent through the proposals for transition of existing cadastral systems to 3D along with legal amendments improving national 3D Cadastre legislation. Concurrently the use of appropriate data sources and the correct depiction of 3D property units’ boundaries and spatial relationships need to be addressed. Spatial relations and constraints amongst real world objects could be modeled geometrically and topologically utilizing numerous modeling tools, e.g. CityGML, BIM and further sophisticated 3D software or by adapting international standards, e.g. LADM. A direct correlation between legal and physical property should be based on consistent geometry between physical and legal space, improving the accuracy that legal spaces’ volumes or locations are defined. To address these issues, this paper investigates correlation possibilities and constraints between legal and physical space of typical 3D property cases. These cases comprise buildings or their interior spaces with mixed use, as well as complex structures described by explicit facade patterns, generated by procedural or by BIM ready 3D models. The 3D models presented are evaluated, regarding compliancy to physical or legal reality.
The existing 2D cadastral systems worldwide cannot provide a proper registration and representation of the land ownership rights, restrictions and responsibilities in a 3D context, which appear in our complex urban environment. Ιn such instances, it may be necessary to consider the development of a 3D Cadastre in which proprietary rights acquire appropriate three-dimensional space both above and below conventional ground level. Such a system should contain the topology and the coordinates of the buildings' outlines and infrastructure. The augmented model can be formed as a full 3D Cadastre, a hybrid Cadastre or a 2D Cadastre with 3D tags. Each country has to contemplate which alternative is appropriate, depending on the specific situation, the legal framework and the available technical means. In order to generate a 3D model for cadastral purposes, a system is required which should be able to exploit and represent 3D data such as LiDAR, a remote sensing technology which acquires three-dimensional point clouds that describe the earth’s surface and the objects on it. LiDAR gives a direct representation of objects on the ground surface and measures their coordinates by analyzing the reflecting light. Moreover, it provides very accurate position and height information, although direct information about the objects’ geometrical shape is not conveyed. In this study, an experimental implementation of 3D Cadastre using LiDAR data is developed, in order to investigate if this information can satisfy the specifications that are set for the purposes of the Hellenic Cadastre. GIS tools have been used for analyzing DSM and true orthophotos of the study area. The results of this study are presented and evaluated in terms of usability and efficiency.