Floor plan extraction from digital building models

Room: Auditorium B
Academic Track 🎓

Sunday, 14:05
Duration: 5 minutes (plus Q&A)

short paper - pdf


video on media.ccc.de

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  • Helga Tauscher
  • Subhashini Krishnakumar

As part of a larger endeavour to make floor plan representations from building models available for indoor map and navigation services, we study the integration of IFC and OSM.

Introduction, background, motivation

Official geo data is increasingly published not only in the form of 2D maps, but also in 3D, mainly as city models in CityGML. Usually the outer shell of buildings is captured in such models, but they may also involve more intricate detail. Even more detailed building models are generated during the planning process for new buildings and renovations. These are nowadays produced in digital form, archived in as-built phase by owners and operators for the life time of a building and, in the future, may even be required to be submitted for building permits.

At the same time there is an increasing public interest in detailed information about public and semi-public interior spaces, for example about their accessibility, localization of barriers or targets (e.g. contact persons in public administration, shops in malls, booths on fairs, markets or larger info events, departments or hospital wards) or resources (e.g. books in libraries, charging stations, fire equipment or defibrillators) or to get a first impression in advance (e.g. virtual open day). The interest and the points of interest may be temporary or permanent.

Since the context of creating and capturing geo data and building data is fundamentally different, there is hardly any integration. Indoor data for maps and navigation models is manually captured or at best derived in undocumented multi-step semi-automatic workflows.

Aim and purpose of the study

The project "Level Out" sets out to develop automated methods and services to make detailed indoor data from digital building models selectively available for the population of city models, map and navigation services (in the form of 2,5 D floorplans).

Towards this end, we are developing a platform to check building models whether they are suitable and contain required data, extract selected and simplified indoor data and convert it into various formats: CityGML LOD0 (Indoor), IndoorGML and OSM Indoor. As input we rely on data in the format IFC (Industry Foundation Classes), the most widespread standard format for digital building models. Indoor OSM, in particular geometry with Simple Indoor Tagging, is one of the various extraction targets. The data created may not be directly fed into OpenStreetMap, but serve as a viable base for further mapping.

There are already older solutions, e.g. BIMServerOsmSerializer (<https://github.com/BIMDataHub/BIMServerOsmSerializer>), which are only built for a version of IFC, which has been a long time standard version, but currently approaches towards its end of life: IFC2x3. There are also solutions under active development, e.g. the JOSM plugin "Indoor Helper" (<https://wiki.openstreetmap.org/wiki/JOSM/Plugins/indoorhelper>), which, however, lack some general approach on the IFC side and coverage of the heterogeneous options to represent geometry in the IFC schema. With this research and development we aim to provide a workflow and software to systematically access floorplan data in IFC.


We start from both ends of integration by looking at the detailed structures of the source and target models in parallel.

From the group of target models, we derive a common model, which will have, at best, near-trivial mappings to OSM Indoor, CityGML, IndoorGML. Although not strictly necessary for the IFC-to-OSM conversion case or any other bilateral integration, the intermediate model will not only allow to tackle integration of IFC with multiple targets besides OSM, but also integration of OSM with multiple sources besides IFC.

Next, we identify relevant information in the source model. IFC exposes a wide variety of geometry modelling constructions from CAD software, mainly following the modelling paradigm of constructive solid geometry (CSG). So far, we found the following principle representation options:

a) Direct floorplan representation in 2.5D: Here we have 2D representations located in 3D space, usually located at the level of the floor finish for a particular storey. There are two versions to be distinguished: space boundaries versus abstract representations of space-defining elements.

b) Extraction from CSG: Spaces (as well as constructive elements) are often represented as solids resulting from extrusion of a planar shape. If extruded in z-direction, the base shape can be extracted and used as 2.5-D representation.

c) Projection onto floor level: If the geometry is not in CSG-form with extrusions, but in BREP (boundary representation), then projection followed by a simplification of the projection result is a possible way to extract.

In addition to the geometric elements, there are semantic elements connected to the geometry that are connected themselves and can be used to charge the geometric model elements with meaning. Depending on the geometry extraction method, correlation and consideration of semantic elements is more evident or complicated - hence possible to different degrees. The paper will discuss these implications.

After identification of the relevant entities, we are developing a three stage process for the actual population of target models from IFC.

  1. Building model enrichment: Information that can be represented in IFC will be played back to the building model instead of being promoted to the generic model only.
  2. Building to intermedite model: This essential step is coved with a flexible rule-based mapping.
  3. Intermediate model to target models: Following a careful design of the generic model, this step should be simple.

We are testing the processes with data from public buildings, two sets of university campus buildings as well as one newly built municipal administration centre. From assessment of the original building data, we will also develop modelling and export guidelines for BIM software. As far as possible, the demo data will be made available publicly as open data. More important, the conversion procedures will be published open source and a respective conversion service will be offered online.


In summary, our work provides practical benefit in terms of tools to support the mapping process as well as a scientific contribution in terms of spatial data integration and expert involvement via domain-specific languages.

The practical benefit of the conversion seems obvious: Building owners can publish data of their publicly accessible spaces to help with volunteer mapping work. In the future we will also tackle update, checking and comparison with existing OSM indoor data.

Scientific contributions are also made in different ways: First, an application scenario for the OGC Indoor Feature Model is provided and - interesting for the audience of this conference - evaluation of how OSM data fits with the generalized model. Further, we explore methods for flexible data integration with domain specialist and expert community involvement. Finally, but beyond the scope of this conference, the applicability of integration methods for bidirectional integration with multiple sources and targets via intermediary formats is evaluated.