3D city model
3D city models support presentation, exploration, analysis, and management tasks in a large number of different application domains.
In particular, 3D city models allow "for visually integrating heterogeneous geoinformation within a single framework and, therefore, create and manage complex urban information spaces.
[7] It mostly follows the CityGML data model, but aims to be developer- and user-friendly by avoiding most of the complexities of its usual GML encoding.
They provide a high level of detail, possible not required by 3D city model applications, but can be incorporated either by exporting their geometry or as encapsulated objects.
In practice, 3D models of buildings of urban regions are generated based on capturing and analyzing 3D point clouds (e.g., sampled by terrestrial or aerial laser scanning) or by photogrammetric approaches.
"Since fully automatic image understanding is very hard to solve, semi-automatic components are usually required to at least support the recognition of very complex buildings by a human operator.
[23] Service-oriented architectures (SOA) for visualizing 3D city models offer a separation of concerns into management and rendering and their interactive provision by client applications.
[25] SOA-based approaches can be distinguished into two main categories, currently discussed in the Open Geospatial Consortium: A map-based technique, the "smart map" approach, aims at providing "massive, virtual 3D city models on different platforms namely web browsers, smartphones or tablets, by means of an interactive map assembled from artificial oblique image tiles.
Most importantly, the map-based approach allows for distributing and using complex 3D city models with having to stream the underlying data to client devices - only the pre-generated map tiles are sent.
This way, "(a) The complexity of the 3D city model data is decoupled from data transfer complexity (b) the implementation of client applications is simplified significantly as 3D rendering is encapsulated on server side (c) 3D city models can be easily deployed for and used by a large number of concurrent users, leading to a high degree of scalability of the overall approach.
