INTERGEO Agenda - english

The BIM Fit Check is an interactive challenge format organised by buildingSMART Deutschland in which software vendors demonstrate that their products correctly implement open BIM standards for carefully defined use cases. In 2025, two events tested IFC georeferencing in practice. The first round took place on 8 May 2025 at the 22nd buildingSMART Anwendertag in Essen. Six software products were asked to correctly encode and decode a georeferenced IFC 4.3 model combining a horizontal CRS (ETRS89 / UTM Zone 32N) with a vertical datum (DHHN2016). The scenario mirrors a common infrastructure handover: an engineering firm exports a model with a specific spatial context, and the receiving software must interpret it without any prior coordinate convention agreement. Participants were assessed on their use of IfcProjectedCRS and IfcRigidOperation, the IFC 4.3 mechanism for positioning a project within a recognised CRS. All six passed. The second round was held on 23 September 2025 at the international buildingSMART Summit in Berlin. Alongside a parallel alignment exchange track, three vendors extended the georeferencing scenario with additional test cases. Both rounds produced a consistent set of findings. The IFC specification gives no clear guidance on when to use IfcMapConversion versus IfcRigidOperation. Both are coordinate operation subtypes, but they address different situations: IfcMapConversion transforms an arbitrary local engineering coordinate system into a projected CRS, while IfcRigidOperation applies a translation offset for projects already working within a recognised CRS. Without normative guidance, implementations diverged even among products that passed the check. IfcProjectedCRS has a structural gap too: it holds only a free-text VerticalDatum string, with no way to reference a compound CRS combining distinct horizontal and vertical components. That is a routine requirement in infrastructure projects, as the ETRS89/DHHN2016 scenario in the check itself demonstrates. Backwards compatibility also remains a problem. The LoGeoRef30 approach, which encodes a project base point through IfcSite.ObjectPlacement without any CRS declaration, stays valid in IFC 4.3 alongside LoGeoRef50. The findings propose resolving this at the MVD level: a Modern MVD would require LoGeoRef50 or higher, while a Legacy MVD would permit LoGeoRef30 for migration scenarios.