An increasing number of cities are creating 3D city models to support visualization and simulations in the urban planning process. The 3D city models are often extended with planned buildings. One way to facilitate this is to add simplified building information modelling (BIM) models of the planned buildings to the 3D city model. This article summarizes some of the recent academic and industrial studies of this topic.

There are several commercial and open-source tools for integrating BIM data into 3D city models. The integration is complicated, as it requires transformation between different information models (ontologies), e.g. between the open BIM format Industry Foundation Classes (IFC) and the open 3D city model format CityGML. The transformation of geometries is also challenging and includes a conversion from solid modelling (used in BIM) to boundary representations (used in city models).

In 2019, a GeoBIM benchmark was launched to study the interoperability in the GeoBIM domain, where GeoBIM stands for an integration between city models and BIM. The benchmark – which was coordinated by the 3D Geoinformation Group at TU Delft, the Netherlands – focused on the interoperability of tools implementing the CityGML and IFC standards, as well as on tools for conversion between the standards. For the latter, some extract, transform & load (ETL) scripts (mainly from Safe Software) were evaluated, and several software tools were tested on four datasets. One conclusion drawn is the problem that IFC files are modelled in different and incompatible manners in terms of the IFC elements that are used and their structure. This makes it challenging to write generic programs to convert IFC data to proper CityGML models. In addition, most IFC elements in the benchmark were translated into generic CityGML objects, which in practice would require manual inspection and modification. To tackle these challenges, the architecture, engineering and construction (AEC) domain needs to reach consensus on the standards and guidelines concerning how to model IFC models (such work has been conducted at national level in several countries). More efforts are also required to standardize the city models. Note that the latest version of CityGML (3.0, which was approved at conceptual level in September 2021) introduces some concepts to improve its interoperability with IFC.

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