Integration of 3D city model and sensor observations based on international open standards

Smart cities effectively integrates human, physical and digital systems operating in the built environment to provide automatic and efficient applications. While 3D city and landscape modelling, Internet of Things (IoT), and domain models are essential techniques of smart cities, the integration of IoT sensor observations and 3D city models is a central information backbone for smart city cyber-infrastructures. However, we argue that most of the existing solutions integrating 3D city models and sensor observations are usually customized and lack of interoperability. In order to improve the interoperability between smart city modules, this study first utilizes 3D city model and IoT web service open standards, and then analyzes integration strategies as well as their pros and cons. In general, we have identified three main strategies: (1) embeddedness approach, (2) external reference approach, and (3) external join approach. These strategies are implemented by integrating the Open Geospatial Consortium (OGC) CityGML and IndoorGML 3D city models and the OGC SensorThings API web service. As the CityGML and IndoorGML models provide 3D building geometry for visualization and indoor networks for navigation, the SensorThings API service provides sensor observations from IoT devices. Finally, based on the implementation, the advantages and disadvantages of each strategy are analyzed by comparing their data sizes and display performance.