The use of 3D city models is changing from visualization to complex use cases where they act as 3D base maps. This requires links to registers and continuous updating of the city models. Still, most models never change or are recreated instead of updated. This study identifies obstacles to version management of 3D city models and proposes recommendations to overcome them, with a main focus on the municipality perspective, foremost in the planning and building processes. As part of this study, we investigate whether national building registers can control the version management of 3D city models. A case study based on investigations of standards, interviews and a review of tools is presented. The study uses an architectural model divided into four layers: data collection, building theme, city model and application. All layers require changes when implementing a new versioning method: the data collection layer requires restructuring of technical solutions and work processes, storage of the national building register requires restructuring, versioning capabilities must be propagated to the city model layer, and tools at the application layer must handle temporal information better. Strong incentives for including versioning in 3D city models are essential, as substantial investment is required to implement versioning in all the layers. Only capabilities required by applications should be implemented, as the complexity grows with the number of versioning functionalities. One outcome of the study is a recommendation to link 3D city models more closely to building registers. This enables more complex use in, e.g., building permits and 3D cadastres, and authorities can fetch required (versioning) information directly from the city model layer.
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