Speckle → IFC 4.3 Exporter (Revit)

🚧 Project Status: WIP

Hey there! This project is still under active development, so expect changes, bugs, and incomplete features. If you have any questions or suggestions, don’t hesitate to reach out at: nikos@speckle.systems

A Speckle Automate function that converts Speckle models from Revit into IFC 4X3 files using ifcopenshell. This exporter is specifically designed for models sent to Speckle from Autodesk Revit and relies on Revit-specific object structures, categories, and parameters.

⚠️ Note on Model Uploads

Large models (greater than 200MB) may fail to upload due to current file size limitations. The team is actively working on resolving this issue.

What It Does

The exporter receives a Speckle model version, walks its object tree, and produces a standards-compliant IFC 4.3 file. Each Speckle object becomes an IFC element with:

• Correct IFC entity classification (IfcWall, IfcSlab, IfcColumn, etc.)
• Tessellated geometry (IfcPolygonalFaceSet)
• Curve geometry for Lines, Arcs, and Polycurves (IfcIndexedPolyCurve with IfcLineIndex/IfcArcIndex)
• Material colours from Speckle render materials
• Revit property sets (Common psets, instance/type parameters, material quantities)
• IFC type objects (IfcWallType, IfcSlabType, etc.) shared across instances
• Spatial structure (IfcProject > IfcSite > IfcBuilding > IfcBuildingStorey)
• IfcSpace elements aggregated under storeys with Room properties
• Automatic skipping of analytical/energy categories (e.g. Energy Analysis, MEP Analytical, Solar Shading)

Pipeline Overview

Speckle Model
    │
    ▼
1. Receive version (specklepy)
    │
    ▼
2. Build definition map (for instance geometry reuse)
    │
    ▼
3. Create IFC scaffold (Project → Site → Building)
    │
    ▼
4. Traverse object tree
    │   For each leaf element:
    │   ├── Classify → IFC entity class (skip analytical categories)
    │   ├── Convert geometry → IfcPolygonalFaceSet or IfcIndexedPolyCurve
    │   ├── Create IFC element + placement
    │   ├── Write property sets & quantities
    │   └── Assign IFC type object
    │
    ▼
5. Flush spatial containment & type relationships
    │
    ▼
6. Write .ifc file

Module Structure

File	Purpose
main.py	Entry point, orchestrates the full pipeline
utils/traversal.py	Walks the Speckle Collection tree (Project > Level > Category > Element)
utils/mapper.py	Classifies Speckle objects into IFC entity types
utils/helpers.py	Shared utilities (_get safe accessor, MM_SCALES unit conversion)
utils/geometry.py	Converts Speckle meshes to IfcPolygonalFaceSet geometry (handles nested BrepX)
utils/curves.py	Converts Lines, Arcs, and Polycurves to IfcIndexedPolyCurve geometry
utils/instances.py	Handles InstanceProxy objects with shared geometry (IfcMappedItem), content-based deduplication
utils/properties.py	Writes IFC property sets and quantities from Revit parameters
utils/type_manager.py	Creates and caches IfcTypeObjects (IfcWallType, etc.)
utils/materials.py	Maps Speckle render materials to IfcSurfaceStyle colours
utils/writer.py	Creates the IFC file scaffold and manages storey creation
utils/receiver.py	Connects to Speckle server and receives model data (uses .env)

Mapping Logic

Classification of Speckle objects to IFC entity types follows a priority chain. The first match wins.

Priority 1: builtInCategory (OST_ enum)

The most reliable source. Read from obj.properties.builtInCategory, which contains the Revit BuiltInCategory enum value.

Examples:

builtInCategory	IFC Class
OST_Walls	IfcWall
OST_Floors	IfcSlab
OST_StructuralColumns	IfcColumn
OST_StructuralFraming	IfcBeam
OST_Doors	IfcDoor
OST_Windows	IfcWindow
OST_Roofs	IfcRoof
OST_CurtainWallPanels	IfcCurtainWall
OST_DuctCurves	IfcDuctSegment
OST_PipeCurves	IfcPipeSegment
OST_PipeFitting	IfcPipeFitting
OST_PlumbingEquipment	IfcSanitaryTerminal
OST_Rebar	IfcReinforcingBar
OST_StructConnections	IfcMechanicalFastener
OST_LightingFixtures	IfcLightFixture
OST_Furniture	IfcFurnishingElement
OST_Rooms	IfcSpace

The full table covers ~70 Revit categories across Architectural, Structural, MEP (HVAC, Plumbing, Electrical), and Site/Civil disciplines.

Skipped Categories

The following analytical/energy OST categories are automatically skipped (not exported to IFC):

OST_MEPLoadAreaSeparationLines, OST_EnergyAnalysisZones, OST_EnergyAnalysisSurface, OST_SolarShading, OST_MEPAnalyticalPipeSegments, OST_MEPAnalyticalDuctSegments, OST_MEPAnalyticalSpaces, OST_ElectricalConduitAnalyticalLines, OST_MEPLoadBoundaryLines, OST_FlowTerminalSeparationLines

Priority 2: Category name (display string)

The category name from the traversal context (the name of the parent Collection in the Speckle tree). Exact match first, then case-insensitive substring match.

Examples:

Category Name	IFC Class
Walls	IfcWall
Structural Columns	IfcColumn
Plumbing Fixtures	IfcSanitaryTerminal
Structural Rebar	IfcReinforcingBar
Structural Connections	IfcMechanicalFastener
Lighting Fixtures	IfcLightFixture

Priority 3: obj.category field

Same lookup as Priority 2, but using the object's own category attribute.

Fallback

If none of the above match, the object is classified as IfcBuildingElementProxy.

Geometry Handling

Direct Meshes (Path B1)

Objects with displayValue containing Mesh objects are converted directly:

1. Extract vertices and faces from each mesh in displayValue (recursively handles nested BrepX/Brep objects)
2. Scale vertices to millimetres based on the mesh's unit declaration
3. Deduplicate vertices via snap grid (0.01mm tolerance) to avoid IFC GEM111 errors
4. Round vertex coordinates to 0.001mm precision for smaller IFC file output
5. Build IfcPolygonalFaceSet with IfcCartesianPointList3D + IfcIndexedPolygonalFace
6. Compute bounding box origin incrementally for IfcLocalPlacement, offset vertices relative to it

Instance Objects (Path A / B2)

Speckle InstanceProxy objects reference shared definition geometry via definitionId. The exporter supports two formats:

• Revit format: definitionId is a 64-char hex hash; geometry is found by walking the object tree
• IFC format: definitionId starts with DEFINITION:; geometry is in definitionGeometry collection

Performance optimisation: geometry is built once as an IfcRepresentationMap, then each instance references it via IfcMappedItem + IfcCartesianTransformationOperator3DnonUniform. This avoids duplicating vertex data across hundreds of identical elements. Content-based hashing further deduplicates definitions that share identical geometry.

Curve Geometry (Path B3)

Objects whose displayValue contains Objects.Geometry.Line, Objects.Geometry.Arc, or Objects.Geometry.Polycurve items (and no meshes or instances) are exported as curve geometry using native IFC curve types:

• Lines → IfcLineIndex segments (start/end points)
• Arcs → IfcArcIndex segments (start/mid/end points)
• Polycurves → Mixed IfcLineIndex and IfcArcIndex segments from the polycurve's segment list (supports Line, Arc, and Polyline sub-segments)

All curves use IfcIndexedPolyCurve with IfcCartesianPointList3D for compact, deduplicated point storage. The representation uses RepresentationType="Curve3D".

Composite Objects (Path B2 — merged instances)

Objects like Windows and Doors may have multiple InstanceProxy items in their displayValue (e.g. frame, glass, sill). These are not separate IFC elements — all instance geometries are merged into a single IfcShapeRepresentation with combined IfcMappedItem entries, producing one IFC element per Speckle object.

Property Sets

The exporter writes property sets matching Revit's native IFC export structure:

Property Set	Content
Pset_<Entity>Common	Standard IFC properties: Reference, IsExternal, LoadBearing, ThermalTransmittance
Pset_SpaceCommon	Room-specific: Reference, RoomNumber, RoomName, Category (Occupant)
RVT_InstanceParameters	All Revit instance parameters
RVT_Identity	Family, Type, ElementId, BuiltInCategory

Quantities

Quantities follow the IFC standard naming convention: Qto_<EntityType>BaseQuantities and Qto_<MaterialName>BaseQuantities.

Quantity Set	Content
Qto_<EntityType>BaseQuantities	Element-level quantities from Revit computed parameters (area, volume, length, width, height, perimeter)
Qto_SpaceBaseQuantities	Room quantities: NetFloorArea, NetVolume
Qto_<MaterialName>BaseQuantities	Per-material quantities: GrossArea, GrossVolume, Density

Element Quantity Mapping

IFC Quantity	Revit Parameter(s)
GrossArea	HOST_AREA_COMPUTED
GrossVolume	HOST_VOLUME_COMPUTED
Length	CURVE_ELEM_LENGTH, INSTANCE_LENGTH_PARAM
Height	WALL_USER_HEIGHT_PARAM, FAMILY_HEIGHT_PARAM, INSTANCE_HEAD_HEIGHT_PARAM
Width	INSTANCE_WIDTH_PARAM, FURNITURE_WIDTH, FLOOR_ATTR_THICKNESS_PARAM
Perimeter	HOST_PERIMETER_COMPUTED

Supported Entity Qto Sets

Qto_WallBaseQuantities, Qto_SlabBaseQuantities, Qto_ColumnBaseQuantities, Qto_BeamBaseQuantities, Qto_DoorBaseQuantities, Qto_WindowBaseQuantities, Qto_RoofBaseQuantities, Qto_CoveringBaseQuantities, Qto_RailingBaseQuantities, Qto_StairBaseQuantities, Qto_RampBaseQuantities, Qto_MemberBaseQuantities, Qto_FootingBaseQuantities, Qto_CurtainWallBaseQuantities, Qto_BuildingElementProxyBaseQuantities, Qto_PipeFittingBaseQuantities, Qto_SanitaryTerminalBaseQuantities, Qto_ReinforcingElementBaseQuantities, Qto_MechanicalFastenerBaseQuantities

IfcSpace (Rooms)

Revit Rooms (OST_Rooms) are exported as IfcSpace elements with special handling:

• Spatial relationship: Aggregated under IfcBuildingStorey via IfcRelAggregates (not contained)
• Naming: Uses the Speckle object name attribute (not Family:Type which is "none:none" for rooms)
• IfcSpace.Name: Set to ROOM_NUMBER
• IfcSpace.LongName: Set to ROOM_NAME
• Geometry: Converted from displayValue meshes like any other element

Function Inputs

Input	Description
file_name	Output IFC filename (timestamp is appended automatically)
IFC_PROJECT_NAME	Name for the IfcProject entity
IFC_SITE_NAME	Name for the IfcSite entity
IFC_BUILDING_NAME	Name for the IfcBuilding entity

Environment Variables

For local testing via receiver.py, configure a .env file:

Variable	Description
SPECKLE_SERVER_URL	Speckle server URL (default: https://app.speckle.systems)
SPECKLE_TOKEN	Personal access token for authentication
SPECKLE_PROJECT_ID	Project (stream) ID

Testing

Model Name	Revit Size	IFC Size	Conversion Time
Huge confidential model	450 MB	391 MB	2h 30m
Snowdon Towers (Architecture)	93.2 MB	118 MB	8m 37s
Speckle Tower	51 MB	45 MB	3m
Rac Basic Sample Model	18.8 MB	12 MB	12s

Resources

• Speckle Developer Docs
• ifcopenshell Documentation
• IFC 4.3 Schema
• Revit BuiltInCategory Reference