8.20.3.10 IfcFaceSurface

8.20.3.10.1 Semantic definition

The IfcFaceSurface defines the underlying geometry of the associated surface to the face.

NOTE Definition according to ISO/CD 10303-42:1992 A face surface is a subtype of face in which the geometry is defined by an associated surface. The portion of the surface used by the face shall be embeddable in the plane as an open disk, possibly with holes. However, the union of the face with the edges and vertices of its bounding loops need not be embeddable in the plane. It may, for example, cover an entire sphere or torus. As both a face and a geometric surface have defined normal directions, a BOOLEAN flag (the orientation attribute) is used to indicate whether the surface normal agrees with (TRUE) or is opposed to (FALSE) the face normal direction. The geometry associated with any component of the loops of the face shall be consistent with the surface geometry, in the sense that the domains of all the vertex points and edge curves are contained in the face geometry surface. A surface may be referenced by more than one face surface.

Informal Propositions

The domain of the face surface is formally defined to be the domain of its face geometry as trimmed by the loops, this domain does not include the bounding loops.
A face surface has non zero finite extent.
A face surface is a manifold.
A face surface is arcwise connected.
A face surface has surface genus 0.
The loops are not part of the face domain.
Loop geometry shall be consistent with face geometry. This implies that any edge - curves or vertex points used in defining the loops bounding the face surface shall lie on the face geometry.
The loops of the face shall not intersect.

8.20.3.10.2 Entity inheritance

8.20.3.10.3 Attributes

#	Attribute	Type	Description
IfcRepresentationItem (2)
	LayerAssignment	SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems	Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items. IFC2x3-CHANGE The inverse attribute LayerAssignments has been added. IFC4-CHANGE The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.
	StyledByItem	SET [0:1] OF IfcStyledItem FOR Item	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. IFC2x3-CHANGE The inverse attribute StyledByItem has been added.
IfcFace (2)
1	Bounds	SET [1:?] OF IfcFaceBound	Boundaries of the face.
	HasTextureMaps	SET [0:?] OF IfcTextureMap FOR MappedTo	No description available.
Click to show 4 hidden inherited attributes
IfcFaceSurface (2)
2	FaceSurface	IfcSurface	The surface which defines the internal shape of the face. This surface may be unbounded. The domain of the face is defined by this surface and the bounding loops in the inherited attribute SELF\FaceBounds.
3	SameSense	IfcBoolean	This flag indicates whether the sense of the surface normal agrees with (TRUE), or opposes (FALSE), the sense of the topological normal to the face.

Table 8.20.3.10.A

8.20.3.10.4 Formal representation

 ENTITY IfcFaceSurface
 SUPERTYPE OF (ONEOF
	(IfcAdvancedFace))
 SUBTYPE OF (IfcFace);
	FaceSurface : IfcSurface;
	SameSense : IfcBoolean;
END_ENTITY;