8.8.3.47 IfcTriangulatedFaceSet
8.8.3.47.1 Semantic definition
The IfcTriangulatedFaceSet is a tessellated face set with all faces being bound by triangles. The faces are constructed by implicit polylines defined by three Cartesian points. Depending on the value of the inherited attribute Closed the instance of IfcTriangulatedFaceSet represents:
- if TRUE, a boundary representation (or B-rep);
- if FALSE, a face based surface representation.
The coordinates of each point are provided by a one-based index into an ordered list of Cartesian points provided by the two-dimensional list CoordIndex, where
- the first dimension of the two-dimensional list addresses the list of triangular faces;
- the second dimension of the two-dimensional list provides exactly three indices. Each index points to a Cartesian point being a vertex of the triangle.
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 8.8.3.47.A for the handling of point index.
See Figure 8.8.3.47.B for using the IfcTriangulatedFaceSet without (as default) and with using the PnIndex.
Optionally normals can be provided. Only normals per vector are supported allowing for visually curved triangles when the three normals of the corresponding three vertices of a triangle are not co-linear to the normal of the triangular face. If they are identical, normals shall be omitted.
In case of a body representation having triangular faces with curvature, different normals for all three vertices in context of this triangles are exported, describing the curvature for smooth visualisation. In case of triangular faces with no curvature, the three vertex-based normals are identical and could always be computed from the face. Therefore vertices should only be exported to support smooth visualisation by curvature of triangles. In case of faceted representation no vertices should be exported.Normals are provided by the two-dimensional list Normals, where
- the first dimension of the two-dimensional list addresses the corresponding list of vertex indices of the triangular faces;
- the second dimension of the two-dimensional list provides exactly three real values to determine the direction of the normal at this vertex of the triangle.
The indices in the CoordIndex point into the list of Normals. The indices of CoordIndex are applied to both points, either directly directly, or via the PnIndex and normals. See Figure 8.8.3.47.C for handling of normals.
Figure 8.8.3.47.D shows the use of IfcTriangulatedFaceSet without annotation. The diagram of the IfcTriangulatedFaceSet represents the indices and the ordered list into which the indices point. The index starts with 1 (indexed as 1 to N), if the greatest index in CoordIndex in N, then the IfcCartesianPointList shall have N lists of 3:3 coordinates.
Figure 8.8.3.47.D shows an IfcTriangulatedFaceSet represented by:
CoordIndex:
((1,6,5), (1,2,6), (6,2,7), (7,2,3), (7,8,6), (6,8,5), (5,8,1), (1,8,4), (4,2,1), (2,4,3), (4,8,7), (7,3,4))
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.))
Informal Propositions
- 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 boundaries of faces;
- the topological normal at each point on the boundary of the triangulated face set shall point away from the material of the solid.
8.8.3.47.2 Entity inheritance
-
- IfcTessellatedItem
- IfcAnnotationFillArea
- IfcBooleanResult
- IfcBoundingBox
- IfcCartesianPointList
- IfcCartesianTransformationOperator
- IfcCsgPrimitive3D
- IfcCurve
- IfcDirection
- IfcFaceBasedSurfaceModel
- IfcFillAreaStyleHatching
- IfcFillAreaStyleTiles
- IfcGeometricSet
- IfcHalfSpaceSolid
- IfcLightSource
- IfcPlacement
- IfcPlanarExtent
- IfcPoint
- IfcSectionedSpine
- IfcSegment
- IfcShellBasedSurfaceModel
- IfcSolidModel
- IfcSurface
- IfcTextLiteral
- IfcVector
8.8.3.47.3 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. The inverse attribute LayerAssignments has been added. 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. The inverse attribute StyledByItem has been added. |
|
| IfcTessellatedFaceSet (4) | |||
| 1 | Coordinates | IfcCartesianPointList3D |
An ordered list of Cartesian points used by the coordinate index defined at the subtypes of IfcTessellatedFaceSet. |
| 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. |
|
| * | Dim | IfcDimensionCount |
This attribute is formally derived. The space dimensionality of this geometric representation item, it is always 3. |
| Click to show 6 hidden inherited attributes Click to hide 6 inherited attributes | |||
| IfcTriangulatedFaceSet (5) | |||
| 2 | Normals | OPTIONAL LIST [1:?] OF LIST [3:3] OF IfcParameterValue |
An ordered list of three directions for normals. It is a two-dimensional list of directions provided by three parameter values. * The first dimension corresponds to the vertex indices of the Coordindex * The second dimension has exactly three values, [1] the x-direction, [2] the y-direction and [3] the z-directions |
| 3 | Closed | OPTIONAL IfcBoolean |
Indication whether the face set is a closed shell (TRUE) or an open shell (FALSE). If omitted no such information can be asserted. |
| 4 | CoordIndex | LIST [1:?] OF LIST [3:3] OF IfcPositiveInteger |
Two-dimensional list for the indexed-based triangles, where * The first dimension represents the triangles (from 1 to N) * The second dimension has exactly three values representing the indices to three vertex points (from 1 to 3). The coordinates of the vertices are provided by the indexed list of SELF\IfcTessellatedFaceSet.Coordinates.CoordList. |
| 5 | PnIndex | OPTIONAL LIST [1:?] OF IfcPositiveInteger |
The list of integers defining the locations in the IfcCartesianPointList3D to obtain the point coordinates for the indices withint the CoordIndex. If the PnIndex is not provided the indices point directly into the IfcCartesianPointList3D. |
| * | NumberOfTriangles | IfcInteger |
This attribute is formally derived. Derived number of triangles used for this triangulation. |
8.8.3.47.4 Examples
-
Figure 8.8.3.47.E -
Figure 8.8.3.47.F -
Figure 8.8.3.47.G -
Figure 8.8.3.47.H -
Figure 8.8.3.47.I -
Figure 8.8.3.47.J -
Figure 8.8.3.47.K -
Figure 8.8.3.47.L -
Figure 8.8.3.47.M -
Figure 8.8.3.47.N -
Figure 8.8.3.47.O -
Figure 8.8.3.47.P
8.8.3.47.5 Formal representation
ENTITY IfcTriangulatedFaceSet
SUPERTYPE OF (ONEOF
(IfcTriangulatedIrregularNetwork))
SUBTYPE OF (IfcTessellatedFaceSet);
Normals : OPTIONAL LIST [1:?] OF LIST [3:3] OF IfcParameterValue;
Closed : OPTIONAL IfcBoolean;
CoordIndex : LIST [1:?] OF LIST [3:3] OF IfcPositiveInteger;
PnIndex : OPTIONAL LIST [1:?] OF IfcPositiveInteger;
DERIVE
NumberOfTriangles : IfcInteger := SIZEOF(CoordIndex);
END_ENTITY;