IfcFaceSurface

Semantic definitions at the entity

Entity definition

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.

NOTE Entity adapted from face_surface defined in ISO 10303-42.

HISTORY New entity in IFC2x

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.

Attribute definitions

#	Attribute	Type	Cardinality	Description	B
2	FaceSurface	IfcSurface	[1:1]	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.	X
3	SameSense	IfcBoolean	[1:1]	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.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	B
IfcRepresentationItem
	StyledByItem	IfcStyledItem @Item	S[0:1]	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.	X
IfcTopologicalRepresentationItem
IfcFace
1	Bounds	IfcFaceBound	S[1:?]	Boundaries of the face.	X
IfcFaceSurface
2	FaceSurface	IfcSurface	[1:1]	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.	X
3	SameSense	IfcBoolean	[1:1]	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.	X

Formal representations

XSD Specification

 <xs:element name="IfcFaceSurface" type="ifc:IfcFaceSurface" substitutionGroup="ifc:IfcFace" nillable="true"/>

 <xs:complexType name="IfcFaceSurface">

  <xs:complexContent>

   <xs:extension base="ifc:IfcFace">

    <xs:sequence>

     <xs:element name="FaceSurface" type="ifc:IfcSurface" nillable="true"/>

    </xs:sequence>

    <xs:attribute name="SameSense" type="ifc:IfcBoolean" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcFaceSurface

 SUBTYPE OF (IfcFace);

  FaceSurface : IfcSurface;

  SameSense : IfcBoolean;

END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
IFC4 to IFC4 ADD1
IfcFaceSurface
SameSense	MODIFIED	Type changed from BOOLEAN to IfcBoolean.

	Fläche - Topologie mit expliziter Geometrie
	Face Surface