Urban Digital Twins (UDTs) have emerged as essential tools for managing city operations, forming the basis of smart city solutions. They offer a digital repre-sentation of the physical urban environment, which supports various city applica-tions such as monitoring mobility, air quality, and modelling simulations. To ac-curately represent the physical world, UDTs need to be updated continuously to reflect the changes in the urban environment on time. The Internet of Things (IoT) enables real-time data collection to capture these changes. Combined with 3D city models, IoT allows the interactive visualisation of patterns and trends in UDTs. In this study, we conduct investigations on the requirements for the web visualisation of semantic 3D city models enriched with time-dependent properties from IoT and simulation data. We explore the 3D models and IoT data integration requirements, 4D web visualisation design considerations, and the technical im-plementation requirements for rendering dynamic properties for UDTs applica-tions. The paper also presents a workflow and a web viewer prototype for the 4D visualisation of integrated 3D models and dynamic data.     «

Urban Digital Twins (UDTs) have emerged as essential tools for managing city operations, forming the basis of smart city solutions. They offer a digital repre-sentation of the physical urban environment, which supports various city applica-tions such as monitoring mobility, air quality, and modelling simulations. To ac-curately represent the physical world, UDTs need to be updated continuously to reflect the changes in the urban environment on time. The Internet of Things (IoT) enables real-time...     »