Ifc Syntax Geometry Swept Solid

IFC Syntax : Swept Solid Geometry

IFC carries most building geometry parametrically : a 2D cross-section (a profile) is swept through 3D space to form a solid. This skill covers the swept-solid entities, their attributes, their WHERE rules, and how the result maps to a shape representation.

Applies to IFC2x3, IFC4, and IFC4.3. The directrix family was restructured across versions : see Version Differences.

Quick Reference

The swept-solid idea

A swept solid pairs a profile with a sweep operation. The profile is the cross-section ; the sweep moves it. The profile entities (IfcProfileDef and its subtypes) are covered by ifc-syntax-geometry-profiles ; this skill covers the sweep.

A profile (IfcProfileDef, ProfileType = AREA)
        +
A sweep operation (extrude / revolve / sweep along a curve)
        =
A solid  -->  placed in an IfcShapeRepresentation, type SweptSolid or AdvancedSweptSolid

IfcSweptAreaSolid : the abstract supertype

Verified verbatim (IFC4.3) :

ENTITY IfcSweptAreaSolid
 ABSTRACT SUPERTYPE OF (ONEOF
	(IfcDirectrixCurveSweptAreaSolid
	,IfcExtrudedAreaSolid
	,IfcRevolvedAreaSolid))
 SUBTYPE OF (IfcSolidModel);
	SweptArea : IfcProfileDef;
	Position : OPTIONAL IfcAxis2Placement3D;
 WHERE
	SweptAreaType : SweptArea.ProfileType = IfcProfileTypeEnum.Area;
END_ENTITY;

Supertype chain : IfcRepresentationItem to IfcGeometricRepresentationItem to IfcSolidModel to IfcSweptAreaSolid.

• SweptArea : the profile (the cross-section).
• Position : an OPTIONAL IfcAxis2Placement3D that repositions the solid.
• SweptAreaType rule : the profile MUST have ProfileType = AREA.

ALWAYS give an IfcSweptAreaSolid a profile whose ProfileType is AREA. NEVER sweep a CURVE-type profile into a solid : a CURVE profile sweeps a surface, not a solid, and SweptAreaType rejects it.

IfcExtrudedAreaSolid : the workhorse

The most common solid in any IFC model : walls, slabs, beams, columns, footings. Verified verbatim (IFC4.3) :

ENTITY IfcExtrudedAreaSolid
 SUPERTYPE OF (ONEOF
	(IfcExtrudedAreaSolidTapered))
 SUBTYPE OF (IfcSweptAreaSolid);
	ExtrudedDirection : IfcDirection;
	Depth : IfcPositiveLengthMeasure;
 WHERE
	ValidExtrusionDirection : IfcDotProduct(IfcRepresentationItem() ||
		IfcGeometricRepresentationItem() || IfcDirection([0.0,0.0,1.0]),
		SELF.ExtrudedDirection) <> 0.0;
END_ENTITY;

• ExtrudedDirection : the direction the profile is moved.
• Depth : the distance moved.
• ValidExtrusionDirection : the dot product of ExtrudedDirection with the local Z axis [0,0,1] must be non-zero, that is ExtrudedDirection is NOT perpendicular to local Z.

ALWAYS keep a non-zero Z component in ExtrudedDirection ; the standard value is (0.,0.,1.). NEVER set ExtrudedDirection perpendicular to local Z : the extrusion would have zero projected height and ValidExtrusionDirection rejects it.

IfcRevolvedAreaSolid : revolving a profile

Verified verbatim (IFC4.3) :

ENTITY IfcRevolvedAreaSolid
 SUPERTYPE OF (ONEOF
	(IfcRevolvedAreaSolidTapered))
 SUBTYPE OF (IfcSweptAreaSolid);
	Axis : IfcAxis1Placement;
	Angle : IfcPlaneAngleMeasure;
 DERIVE
	AxisLine : IfcLine := ... ;
 WHERE
	AxisDirectionInXY : Axis.Z.DirectionRatios[3] = 0.0;
	AxisStartInXY : ('IFC4X3_DEV.IFCCARTESIANPOINT' IN TYPEOF(Axis.Location))
		AND (Axis.Location\IfcCartesianPoint.Coordinates[3] = 0.0);
END_ENTITY;

• Axis : the axis the profile is revolved around.
• Angle : the revolution angle.
• AxisLine : DERIVED, never serialized.
• AxisDirectionInXY : the axis direction has zero Z ratio.
• AxisStartInXY : the axis start point has zero Z coordinate.

ALWAYS keep the revolution Axis entirely in the profile's XY plane : both its direction and its start point must have a zero Z component. Used for arches, circular footings, dome-like elements.

The directrix family : sweeping along a curve

A profile can be swept along a 3D curve (a directrix). In IFC4.3 the two directrix-driven sweeps share an abstract supertype. Verified verbatim (IFC4.3) :

ENTITY IfcDirectrixCurveSweptAreaSolid
 ABSTRACT SUPERTYPE OF (ONEOF
	(IfcFixedReferenceSweptAreaSolid
	,IfcSurfaceCurveSweptAreaSolid))
 SUBTYPE OF (IfcSweptAreaSolid);
	Directrix : IfcCurve;
	StartParam : OPTIONAL IfcCurveMeasureSelect;
	EndParam : OPTIONAL IfcCurveMeasureSelect;
 WHERE
	DirectrixBounded : (EXISTS(StartParam) AND EXISTS(EndParam)) OR
		(SIZEOF(['IFC4X3_DEV.IFCCONIC', 'IFC4X3_DEV.IFCBOUNDEDCURVE'] * TYPEOF(Directrix)) = 1);
END_ENTITY;

• IfcSurfaceCurveSweptAreaSolid adds ReferenceSurface (IfcSurface) : the directrix lies on this surface, which orients the profile. Used for curved walls following terrain, road and bridge geometry.
• IfcFixedReferenceSweptAreaSolid adds FixedReference (IfcDirection) : a constant direction that orients the profile so it does not twist with the curve. Used for curved beams, handrails, ducts.

DirectrixBounded : if StartParam or EndParam is omitted, the Directrix must be a bounded or conic curve.

IfcDirectrixCurveSweptAreaSolid is NEW IN IFC4.3 : see Version Differences.

IfcSweptDiskSolid : pipes and rebar

IfcSweptDiskSolid is NOT an IfcSweptAreaSolid : it is a separate subtype of IfcSolidModel. It sweeps a circular disk, not a profile, along a 3D directrix. Verified verbatim (IFC4.3) :

ENTITY IfcSweptDiskSolid
 SUPERTYPE OF (ONEOF
	(IfcSweptDiskSolidPolygonal))
 SUBTYPE OF (IfcSolidModel);
	Directrix : IfcCurve;
	Radius : IfcPositiveLengthMeasure;
	InnerRadius : OPTIONAL IfcPositiveLengthMeasure;
	StartParam : OPTIONAL IfcParameterValue;
	EndParam : OPTIONAL IfcParameterValue;
 WHERE
	DirectrixBounded : (EXISTS(StartParam) AND EXISTS(EndParam)) OR
		(SIZEOF(['IFC4X3_DEV.IFCCONIC', 'IFC4X3_DEV.IFCBOUNDEDCURVE'] * TYPEOF(Directrix)) = 1);
	DirectrixDim : Directrix.Dim = 3;
	InnerRadiusSize : (NOT EXISTS(InnerRadius)) OR (Radius > InnerRadius);
END_ENTITY;

• Radius : the outer radius of the disk. InnerRadius : present makes a hollow tube.
• DirectrixDim : the directrix MUST be 3-dimensional.
• InnerRadiusSize : Radius MUST be strictly greater than InnerRadius.

ALWAYS use IfcSweptDiskSolid for pipes, ducts, and reinforcing bars. ALWAYS give its Directrix a 3D curve.

Mapping to RepresentationType

A swept solid sits in an IfcShapeRepresentation whose RepresentationType is one of two labels :

• SweptSolid : the Items are IfcExtrudedAreaSolid and / or IfcRevolvedAreaSolid instances. The standard label for walls, slabs, beams.
• AdvancedSweptSolid : the Items are IfcSurfaceCurveSweptAreaSolid, IfcFixedReferenceSweptAreaSolid, IfcExtrudedAreaSolidTapered, IfcRevolvedAreaSolidTapered, or IfcSweptDiskSolid. Introduced with IFC4.

ALWAYS label a tapered or directrix-driven sweep AdvancedSweptSolid, never SweptSolid. See ifc-syntax-geometry-representations.

Version Differences

ALWAYS give IfcSweptAreaSolid.Position a value in an IFC2x3 file : it is mandatory there, OPTIONAL only from IFC4. The IFC4.3 IfcDirectrixCurveSweptAreaSolid refactor moved Directrix / StartParam / EndParam into a shared supertype ; the attribute set a reader sees is unchanged.

Decision Trees

Which swept-solid entity?

How is the solid formed?
|
+-- Move a profile in a straight line  --> IfcExtrudedAreaSolid
|   The profile changes along the way (taper)?  --> IfcExtrudedAreaSolidTapered
|
+-- Rotate a profile around an axis  --> IfcRevolvedAreaSolid
|   The profile changes along the way?  --> IfcRevolvedAreaSolidTapered
|
+-- Move a profile along a 3D curve
|   +-- The curve lies on a reference surface  --> IfcSurfaceCurveSweptAreaSolid
|   +-- The profile keeps a fixed up-direction  --> IfcFixedReferenceSweptAreaSolid
|
+-- Sweep a circular disk along a 3D curve (pipe, duct, rebar)
    --> IfcSweptDiskSolid  (NOT an IfcSweptAreaSolid)

SweptSolid or AdvancedSweptSolid?

What entities are in the IfcShapeRepresentation Items?
|
+-- Only IfcExtrudedAreaSolid and / or IfcRevolvedAreaSolid
|   --> RepresentationType = 'SweptSolid'
|
+-- Any tapered, directrix-driven, or swept-disk solid
    --> RepresentationType = 'AdvancedSweptSolid'

Does the directrix need start and end parameters?

Is the Directrix a bounded or conic curve (IfcPolyline, IfcTrimmedCurve, IfcCircle)?
|
+-- YES --> StartParam / EndParam are optional ; DirectrixBounded is satisfied.
|
+-- NO, the directrix is unbounded (a plain IfcLine)
    --> StartParam AND EndParam are BOTH required, or DirectrixBounded fails.

Patterns

Pattern : Extrude a profile into a solid

ALWAYS model a wall, slab, beam, or column as an IfcExtrudedAreaSolid : set SweptArea to an AREA-type profile, ExtrudedDirection to the sweep direction (standard (0.,0.,1.)), and Depth to the distance. ALWAYS keep a non-zero Z component in ExtrudedDirection : the ValidExtrusionDirection rule rejects a direction perpendicular to local Z. NEVER feed a CURVE-type profile : the SweptAreaType rule requires AREA. See ifc-syntax-geometry-profiles for the profile entities.

Pattern : Revolve a profile

ALWAYS model an arch or a circular footing as an IfcRevolvedAreaSolid : set SweptArea to an AREA profile, Axis to an IfcAxis1Placement, and Angle to the revolution angle. ALWAYS keep the Axis direction and start point in the profile's XY plane : both AxisDirectionInXY and AxisStartInXY require a zero Z component.

Pattern : Sweep a profile along a curve

ALWAYS use IfcSurfaceCurveSweptAreaSolid when the sweep follows a curve lying on a surface (a wall following terrain) : set ReferenceSurface to that surface. ALWAYS use IfcFixedReferenceSweptAreaSolid when the profile must keep a constant up-direction along the sweep (a curved handrail) : set FixedReference to that direction. ALWAYS supply StartParam and EndParam when the Directrix is an unbounded curve : DirectrixBounded requires it.

Pattern : Model a pipe or rebar with IfcSweptDiskSolid

ALWAYS model a pipe, duct, or reinforcing bar as an IfcSweptDiskSolid : set Directrix to the 3D centre-line curve and Radius to the outer radius. ALWAYS set InnerRadius for a hollow tube, and keep Radius > InnerRadius : InnerRadiusSize rejects an inner radius equal to or larger than the outer. ALWAYS give the Directrix a 3-dimensional curve : DirectrixDim requires Directrix.Dim = 3.

Pattern : Label the representation correctly

ALWAYS set RepresentationType to SweptSolid when the Items are only IfcExtrudedAreaSolid and IfcRevolvedAreaSolid. ALWAYS set RepresentationType to AdvancedSweptSolid when the Items include a tapered solid, a directrix-driven solid, or an IfcSweptDiskSolid. NEVER label an advanced sweep SweptSolid : an MVD-conformant consumer rejects the mismatched type. See ifc-syntax-geometry-representations.

Pattern : Honour the version differences

ALWAYS give IfcSweptAreaSolid.Position a value in an IFC2x3 file : the attribute is mandatory in IFC2x3 and OPTIONAL only from IFC4. ALWAYS supply StartParam and EndParam on an IfcSweptDiskSolid in an IFC2x3 file : they are mandatory in IFC2x3 and OPTIONAL from IFC4. NEVER use IfcExtrudedAreaSolidTapered, IfcRevolvedAreaSolidTapered, or IfcFixedReferenceSweptAreaSolid in an IFC2x3 file : they were added in IFC4.

Reference Links

• references/methods.md : the verified EXPRESS definitions of every swept-solid entity, the complete WHERE-rule table, the supertype chains, and the per-version difference detail.
• references/examples.md : worked STEP scenarios : an extruded wall, a revolved arch, a swept-disk pipe, a tapered extrusion, and the shape-representation wrapping.
• references/anti-patterns.md : the failure modes this skill prevents, each with the WHERE rule it breaks and the reason it fails.

Official sources

• IfcSweptAreaSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcSweptAreaSolid.htm
• IfcExtrudedAreaSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcExtrudedAreaSolid.htm
• IfcRevolvedAreaSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcRevolvedAreaSolid.htm
• IfcDirectrixCurveSweptAreaSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcDirectrixCurveSweptAreaSolid.htm
• IfcSurfaceCurveSweptAreaSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcSurfaceCurveSweptAreaSolid.htm
• IfcFixedReferenceSweptAreaSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcFixedReferenceSweptAreaSolid.htm
• IfcSweptDiskSolid : https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcSweptDiskSolid.htm

Related skills

• ifc-syntax-geometry-profiles : the IfcProfileDef cross-section entities a swept solid sweeps.
• ifc-syntax-geometry-representations : IfcShapeRepresentation and the RepresentationType values SweptSolid and AdvancedSweptSolid.
• ifc-syntax-geometry-placement : IfcAxis2Placement3D, used for Position.
• ifc-syntax-geometry-brep : explicit boundary-representation geometry, the alternative to a parametric sweep.