IFC 4.3.x development

8.20.3.10 IfcFaceSurface

Change log

IFC4

modificationsattributes SameSense definitionChanged from boolean to IfcBoolean

8.20.3.10.1 Semantic definitions at the entity

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

NOTE  The topology is used to trim the geometry of the surface. There is no need to geometrically trim the surface to match the topology.

 

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:

  1. 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.
  2. A face surface has non zero finite extent.
  3. A face surface is a manifold.
  4. A face surface is arcwise connected.
  5. A face surface has surface genus 0.
  6. The loops are not part of the face domain.
  7. 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.
  8. The loops of the face shall not intersect.

8.20.3.10.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignmentSET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment 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.
IfcTopologicalRepresentationItem
IfcFace
1 Bounds SET [1:?] OF IfcFaceBound Boundaries of the face.
HasTextureMaps SET [0:?] OF IfcTextureMap FOR MappedTo
IfcFaceSurface
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.

8.20.3.10.2 Entity inheritance

dot_inheritance IfcAdvancedFace IfcAdvancedFace IfcFaceSurface IfcFaceSurface IfcAdvancedFace->IfcFaceSurface IfcFace IfcFace IfcFaceSurface->IfcFace IfcTopologicalRepresentationItem IfcTopologicalRepresentationItem IfcFace->IfcTopologicalRepresentationItem IfcTopologicalRepresentationItem_children 6 more... IfcTopologicalRepresentationItem_children->IfcTopologicalRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcTopologicalRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.20.3.10.3 Formal representations

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