IFC 4.3.x development

8.8.3.44 IfcTessellatedFaceSet

Change log

IFC4

added

8.8.3.44.1 Semantic definitions at the entity

The IfcTessellatedFaceSet is a boundary representation topological model limited to planar faces and straight edges. It may represent an approximation of an analytical surface or solid that may be provided in addition to its tessellation as a separate shape representation. The IfcTessellatedFaceSet provides a compact data representation of an connected face set using indices into ordered lists of vertices, normals, colours, and texture maps.

NOTE  The compact representation has been chosen to enable small data sets despite potentially large sets of faces, edges and vertices needed to represent tessellations of analyticals surfaces and solids, and despite large sets of colour and texture information to annotate the tessellated faces.

The IfcTessellatedFaceSet is an abstract supertype of tesselated face sets each imposing specific constraints on face generation for tessellation, such as triangulation (with or without strip and fans), or quadrilaterals, or polygonal faces (with or without inner loops).

NOTE  Not all different constraints on face sets are included as specific subtypes in this release of the specification.

The following attributes apply to all subtypes:

  • The Coordinates are the ordered list of Cartesian points representing the vertices of the tessellated item. An index list, defined at the level of subtypes, uses the points, identified by index position, to construct the polylines that represent the faces.
  • The HasColours inverse relation provides an indexed colour map with an corresponding list of indices providing a colour for each face of the tessellated face set.
  • The HasTextures inverse relation provides an indexed texture map with an corresponding list of indices providing texture coordinates that map to the geometric coordinates of the polylines representing the faces.

Each face of the tessellated face set shall have:

  • at least three non-coincident vertices;
  • vertices that define a planar polygon;
  • vertices that define a non-self-intersecting polygon.

NOTE  The definition of IfcTessellatedFaceSet is based on the indexedFaceSet defined in ISO/IEC 19775-1

HISTORY  New entity in IFC4.

8.8.3.44.1 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.
IfcGeometricRepresentationItem
IfcTessellatedItem
IfcTessellatedFaceSet
1 Coordinates IfcCartesianPointList3D An ordered list of Cartesian points used by the coordinate index defined at the subtypes of IfcTessellatedFaceSet.
Dim INVALID The space dimensionality of this geometric representation item, it is always 3.
HasColours SET [0:1] OF IfcIndexedColourMap FOR MappedTo Reference to the indexed colour map providing the corresponding colour RGB values to the faces of the subtypes of IfcTessellatedFaceSet.
HasTextures SET [0:?] OF IfcIndexedTextureMap FOR MappedTo Reference to the indexed texture map providing the corresponding texture coordinates to the vertices bounding the faces of the subtypes of IfcTessellatedFaceSet.

8.8.3.44.2 Entity inheritance

dot_inheritance IfcPolygonalFaceSet IfcPolygonalFaceSet IfcTessellatedFaceSet IfcTessellatedFaceSet IfcPolygonalFaceSet->IfcTessellatedFaceSet IfcTessellatedItem IfcTessellatedItem IfcTessellatedFaceSet->IfcTessellatedItem IfcTriangulatedFaceSet IfcTriangulatedFaceSet IfcTriangulatedFaceSet->IfcTessellatedFaceSet IfcIndexedPolygonalFace IfcIndexedPolygonalFace IfcIndexedPolygonalFace->IfcTessellatedItem IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcTessellatedItem->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.8.3.44.3 Formal representations

ENTITY IfcTessellatedFaceSet
 ABSTRACT SUPERTYPE OF (ONEOF
	(IfcPolygonalFaceSet
	,IfcTriangulatedFaceSet))
 SUBTYPE OF (IfcTessellatedItem);
	Coordinates : IfcCartesianPointList3D;
 DERIVE
	 Dim : IfcDimensionCount := 3;
 INVERSE
	HasColours : SET [0:1] OF IfcIndexedColourMap FOR MappedTo;
	HasTextures : SET [0:?] OF IfcIndexedTextureMap FOR MappedTo;
END_ENTITY;