IFC for BIM: Exporting Buildings from OpenStreetMap
BIM (Building Information Modeling) has revolutionized building design. But a project doesn't exist in a vacuum — a building stands in an urban environment, next to other buildings, roads, and parks. The development context is critically important during pre-design analysis. OpenStreetMap contains data on millions of buildings worldwide, and osm2cdr.ru can convert them to IFC format — the standard language of BIM.
What Is IFC
IFC (Industry Foundation Classes) is an open international standard for data exchange in the construction industry, defined by ISO 16739. The format is developed by buildingSMART and supported by all major BIM platforms.
Key versions:
- IFC2x3 — most widely adopted, universally supported.
- IFC4 — current version (ISO 16739-1:2018), improved geometry, energy efficiency.
- IFC4.3 — extensions for infrastructure (roads, bridges, tunnels).
IFC describes a building as an object hierarchy: IfcProject -> IfcSite -> IfcBuilding -> IfcBuildingStorey -> IfcWall, IfcSlab, IfcWindow. Each element has geometry, material, properties, and relationships with other elements.
Why BIM Models from OpenStreetMap
Pre-Design Analysis
An architect receives a commission for a building at a specific address. The first step is analyzing the surroundings:
- What buildings stand nearby? How tall are they?
- What is the building density in the block?
- Where do shadows fall? How to ensure adequate sunlight?
- Where are the roads and pedestrian flows?
Exporting from OSM to IFC provides answers in minutes, not days of manual modeling.
Development Context
The BIM model of the designed building is placed in the context of existing development. This enables:
- Checking height regulations.
- Modeling solar exposure and wind flows.
- Assessing the visual impact of the new building on the environment.
- Coordinating architectural decisions with authorities.
Urban Planning Analysis
Working on master plans and zoning regulations requires a model of an entire district or city. OSM is the only free source of such data at the scale of millions of buildings.
LOD Levels of Detail
BIM uses a Level of Development system:
| LOD | Description | Data from OSM |
|---|---|---|
| LOD 100 | Conceptual mass, volume only | Building footprint + height (building=yes) |
| LOD 200 | Approximate geometry, key dimensions | Footprint + floors (building:levels) + height |
| LOD 300 | Accurate geometry, materials | + building:material, roof:shape, roof:material |
| LOD 350 | Detail for coordination | Requires survey (not from OSM) |
| LOD 400 | For fabrication | Design documentation |
| LOD 500 | As-built model | Post-construction |
OSM2CDR exports buildings at LOD 100-200, and when material and roof tags are available, approaches LOD 300. This is sufficient for pre-design analysis and context but does not replace design documentation.
How OSM2CDR Converts Buildings to IFC
Data Sources
The exporter extracts the following OSM building tags:
- building — building type (yes, residential, commercial, industrial).
- building:levels — number of floors (used to calculate height).
- height — exact height in meters.
- building:material — wall material (brick, concrete, wood, glass).
- roof:shape — roof form (flat, gabled, hipped, dome).
- roof:material — roof material (tiles, metal, concrete).
- building:colour — facade color.
- addr:street, addr:housenumber — address.
Conversion Algorithm
- Footprints — building polygons from OSM become IfcBuildingElementProxy.
- Height — if the
heighttag exists, it is used. Otherwisebuilding:levels * 3.0(average floor height). If no data — 9.0 m (3 floors by default). - Extrusion — the footprint is extruded upward to the given height (IfcExtrudedAreaSolid).
- Roof — when roof:shape is available, roof geometry is added.
- Materials — IfcMaterial with visual properties is created from building:material.
- Hierarchy — all buildings are grouped: IfcProject -> IfcSite (with coordinates) -> IfcBuilding.
Coordinate System
The IFC model is exported in a local coordinate system with real geographic coordinates referenced through IfcSite. This allows importing the model into Revit or ArchiCAD with correct geo-positioning.
Import into Revit
- Open Revit, create a new project or open an existing one.
- "Insert" tab -> "Link IFC" or "Open IFC".
- Select the .ifc file exported from osm2cdr.ru.
- Revit will create families for each building.
- If necessary, configure IFC -> Revit category mapping.
Recommendation: use "Link IFC" instead of "Open" so the IFC model remains an external reference and doesn't clutter the project.
Import into ArchiCAD
- Open ArchiCAD.
- "File" -> "Merge" -> select the .ifc file.
- Configure import parameters: coordinate system, element mapping.
- ArchiCAD imports buildings as GDL objects.
ArchiCAD has one of the best IFC import implementations — buildings retain their properties, materials, and hierarchy.
Limitations
- LOD 100-200 — OSM cannot provide interior layouts, facade details, or engineering systems.
- Footprint accuracy — building footprints in OSM are drawn by volunteers with 1-3 meter accuracy.
- Incomplete data — not all OSM buildings have height or building:levels tags. Default values are used in these cases.
- Timeliness — OSM is updated by volunteers; new construction may appear with a delay.
- Not a design replacement — IFC from OSM is suitable for context and analysis, not for working documentation.
Alternative Formats
- CityJSON — compact JSON format for 3D city models, easier to parse programmatically.
- CityGML — OGC XML format for city models, used in government cadastres.
- OBJ/glTF — for visualization in Blender, Three.js, Unreal Engine (without BIM semantics).