3D geographic information about urban objects (buildings, roads) is needed to monitor and control processes within modern urban areas (noise, flooding, energy demand/supply). However, each specific process requires 3D data with its own specific semantic and geometric Level of Detail (LoD), and current approaches require enormous manual efforts to collect general-purpose 3D data and to transform it to make it suitable for a specific application.
In this project, we developed a fundamental solution for providing 3D data at application specific LoDs. For this, we investigated an innovative method beyond the state-of-the-art by developing a 4D data structure to store the multi-LoD knowledge as an extra dimension to the 3D spatial dimensions in an integrated 3D+LoD (4D) model.
We have also developed novel reconstruction methods for 3D urban data at application specific LoDs. This provides the LoDs for the 4D model. Finally, we developed a methodology to compare two existing 3D city models, associate and store them with their correspondences in 4D, as well as a methodology for versioning to extract and update the model using one LoD at a time (as a slice of the 4D model). This opens a new horizon for modelling parametrisable aspects of urban data in one data structure, like temporal aspects. More research is needed to implement the 4D approach in practice. This requires addressing the complexity added to the process by the set of rules needed to enforce the management of the model.
The use case driven project results for the automated reconstruction of application specific 3D+LoD data from different sources and the publication of these countrywide 3D data as open data in our developer friendly-format has made 3D data accessible to many more urban professionals as well as to the wider public. This has significantly increased the use of 3D data in a wide variety of urban applications, such as simulations of energy demand, wind flow, pollutant dispersion, solar energy potential, noise, and the urban heat island effect. By making 3D building models accessible and affordable, they can finally become mainstream and be used in simulations and applications to optimally design, maintain and change urban areas to address global challenges.
