IfcPolygonalFaceSet

Natural language names
Polygonal Face Set
Change log
ItemSPFXMLChangeDescription
IFC4 Addendum 2
    IfcPolygonalFaceSetADDED
Semantic definitions at the entity
Entity definition

The IfcPolygonalFaceSet is a tessellated face set with all faces being bound by polygons. The planar faces are constructed by implicit polylines defined by three or more Cartesian points. Each planar face is defined by an instance of IfcIndexedPolygonalFace, or in case of faces with inner loops by IfcIndexedPolygonalFaceWithVoids.

Depending on the value of the attribute Closed the instance of IfcPolygonalFaceSet represents:

The attribute Faces refers to a list of IfcIndexedPolygonalFace's having an one-based CoordIndex that provides three or more indices. If the face has inner loops, the IfcIndexedPolygonalFaceWithVoids has a two-dimensional, one-based list, where:

Depending on the provision of PnIndex the indices point either directly into the IfcCartesianPointList3D referenced by Coordinates defined at the supertype IfcTessellatedFaceSet, or they point into the PnIndex where the integer values at that position provides the location of the coordinate values within the IfcCartesianPointList3D. See Figure 341 for the handling of point index.

PnIndex

Figure 341 — Use of PnIndex

NOTE  If the IfcPolygonalFaceSet is closed, the face vertices of the IfcIndexedPolygonalFace's shall connect counterclock-wise when seen from the outside of the closed shell to guarantee that the face normal points away from the material of the shell. Inner loops, provided by the IfcIndexedPolygonalFaceWithVoids, shall connect clock-wise.

 

IfcFacetedFaceSet_Example-01

Figure 342 shows an IfcFacetedFaceSet represented by

#1 IfcIndexedPolygonalFace: ((1, 2, 3, 4) #2 IfcIndexedPolygonalFace: ((6, 2, 3, 7) #3 IfcIndexedPolygonalFace: ((7, 3, 4, 8) #4 IfcIndexedPolygonalFace: ((8, 4, 1, 5) #5 IfcIndexedPolygonalFace: ((1, 4, 3, 2) #6 IfcIndexedPolygonalFace: ((6, 7, 8, 5) #7 IfcCartesianPointList3D: ((0.,0.,0.), (1.,0.,0.), (1.,1.,0.), (0.,1.,0.), (0.,0.,2.), (1.,0.,2.), (1.,1.,2.), (0.,1.,2.))

Figure 342 — Polygonal face set geometry

 
NOTE  The definition of IfcFacetedFaceSet is based on the indexedFaceSet defined in ISO/IEC 19775-1
HISTORY  New entity in IFC4 Addendum 2.

Informal Propositions:

  1. If Closed = TRUE, the same topological constraints as imposed by an faceted boundary representation shall be safisfied. In particular:
    • each face shall be unique;
    • each edge shall be used by exactly two outer or inner boundaries of faces;
    • the topological normal at each point on the boundary of the polygonal face set shall point away from the material of the solid.
Attribute definitions
#AttributeTypeCardinalityDescription G
2ClosedIfcBoolean? Indication whether the IfcPolygonalFaceSet is a closed shell or not. If omited no such information can be provided.X
3FacesIfcIndexedPolygonalFaceL[1:?] The list of polygonal faces, with or without inner loops, that bound the faceted face set.X
4PnIndexIfcPositiveInteger? L[1:?] The list of integers defining the locations in the IfcCartesianPointList3D to obtain the point coordinates for the indices at the indexed polygonal faces. If the PnIndex is not provided the indices at the indexed polygonal faces point directly into the IfcCartesianPointList3D.X
Inherited definitions from supertypes
Entity inheritance IfcTessellatedFaceSet IfcTessellatedItem IfcGeometricRepresentationItem IfcRepresentationItem
Attribute inheritance
#AttributeTypeCardinalityDescriptionG
IfcRepresentationItem
LayerAssignmentIfcPresentationLayerAssignment
@AssignedItems
S[0:1]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.
X
StyledByItemIfcStyledItem
@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.
IFC2x3 CHANGE  The inverse attribute StyledByItem has been added.
X
IfcGeometricRepresentationItem
IfcTessellatedItem
IfcTessellatedFaceSet
1CoordinatesIfcCartesianPointList3D An ordered list of Cartesian points used by the coordinate index defined at the subtypes of IfcTessellatedFaceSet.X
HasColoursIfcIndexedColourMap
@MappedTo
S[0:1]Reference to the indexed colour map providing the corresponding colour RGB values to the faces of the subtypes of IfcTessellatedFaceSet.X
HasTexturesIfcIndexedTextureMap
@MappedTo
S[0:?]Reference to the indexed texture map providing the corresponding texture coordinates to the vertices bounding the faces of the subtypes of IfcTessellatedFaceSet.X
Dim
:=3
IfcDimensionCountThe space dimensionality of this geometric representation item, it is always 3. X
IfcPolygonalFaceSet
2ClosedIfcBoolean? Indication whether the IfcPolygonalFaceSet is a closed shell or not. If omited no such information can be provided.X
3FacesIfcIndexedPolygonalFaceL[1:?] The list of polygonal faces, with or without inner loops, that bound the faceted face set.X
4PnIndexIfcPositiveInteger? L[1:?] The list of integers defining the locations in the IfcCartesianPointList3D to obtain the point coordinates for the indices at the indexed polygonal faces. If the PnIndex is not provided the indices at the indexed polygonal faces point directly into the IfcCartesianPointList3D.X
Examples
Formal representations
XML Specification
 <xs:element name="IfcPolygonalFaceSet" type="ifc:IfcPolygonalFaceSet" substitutionGroup="ifc:IfcTessellatedFaceSet" nillable="true"/>
 <xs:complexType name="IfcPolygonalFaceSet">
  <xs:complexContent>
   <xs:extension base="ifc:IfcTessellatedFaceSet">
    <xs:sequence>
     <xs:element name="Faces">
      <xs:complexType>
       <xs:sequence>
        <xs:element ref="ifc:IfcIndexedPolygonalFace" maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcIndexedPolygonalFace"/>
       <xs:attribute ref="ifc:cType" fixed="list"/>
       <xs:attribute ref="ifc:arraySize" use="optional"/>
      </xs:complexType>
     </xs:element>
    </xs:sequence>
    <xs:attribute name="Closed" type="ifc:IfcBoolean" use="optional"/>
    <xs:attribute name="PnIndex" use="optional">
     <xs:simpleType>
      <xs:restriction>
       <xs:simpleType>
        <xs:list itemType="ifc:IfcPositiveInteger"/>
       </xs:simpleType>
      </xs:restriction>
     </xs:simpleType>
    </xs:attribute>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>
EXPRESS Specification
ENTITY IfcPolygonalFaceSet
 SUBTYPE OF (IfcTessellatedFaceSet);
  Closed : OPTIONAL IfcBoolean;
  Faces : LIST [1:?] OF IfcIndexedPolygonalFace;
  PnIndex : OPTIONAL LIST [1:?] OF IfcPositiveInteger;
END_ENTITY;

Link to EXPRESS-G diagram EXPRESS-G diagram

References  References: IfcIndexedPolygonalFace

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