REPRESENTATION OF A 3-D CITY MODEL IN SPATIAL OBJECT-RELATIONAL DATABASES

Three-dimensional city models become more and more important in many GIS applications. Examples are, apart from simple visualization, city and land use planning as well as telecommunication planning and disaster management. Currently, there are no 3-D GIS available, which are suitable for these applications. For managing large spatial data sets in an efficient and sustainable way, spatial databases are suitable, but in general restricted to two dimensions. The paper answers the questions how to represent a 3-D city model in an object-relational spatial database, and to what degree the modeling, analysis and query mechanism of the database can be used for 3-D models and applications. Our geometrical-topological 3-D city model is based on existing standards of the ISO and the Open GIS Consortium to ensure interoperability with other systems and data providers. Recent 'object-relational ' databases support sophisticated object models closing the gap between relational databases and object-oriented models. Furthermore, spatial extensions are available for database systems. Based on the widespread commercial database system Oracle 9.2i Spatial, the functionality and efficiency of analysis, access and queries is examined. In our paper we will demonstrate which kind of 3-D spatial queries are feasible using Oracle Spatial, and how exact the query results are with respect to geometry, especially when using threedimensional spatial indices. Likewise, the system's performance is considered by means of miscellaneous benchmarks and their dependency on individual factors such as the recursive aggregation of objects. 1