2.6.4. Thematic model¶
The thematic model consists of the class definitions for the most important types of objects within virtual 3D city models. Most thematic classes are (transitively) derived from the basic classes Feature and FeatureCollection, the basic notions defined in ISO 19109 and GML3 for the representation of features and their aggregations. Features contain spatial as well as non-spatial attributes, which are mapped to GML3 feature properties with corresponding data types. Geometric properties are represented as associations to the geometry classes described in Section 2.6.1 The thematic model also comprises different types of interrelationships between Feature classes like aggregations, generalizations, and associations.
The aim of the explicit modelling is to reach a high degree of semantic interoperability between different applications. By specifying the thematic concepts and their semantics along with their mapping to UML and GML3, different applications can rely on a well-defined set of Feature types, attributes, and data types with a standardised meaning or interpretation. In order to allow also for the exchange of objects and/or attributes that are not explicitly modelled in CityGML, the concepts of GenericCityObjects and GenericAttributes have been introduced.