8.8.3.48 IfcTriangulatedIrregularNetwork

8.8.3.48.1 Semantic definition

The IfcTriangulatedIrregularNetwork is a triangulated face set for representing horizontal surfaces (one unique Z coordinate for all X and Y coordinates within domain) with additional flags for each face indicating breaklines between faces or designation as a hole or void. Triangles shall be defined with vertices in counterclockwise order as viewing from above (following right-hand rule).

For visualization, applications should not display faces where flags are set as negative (either a hole, void, or possible future extension).

The flag Void shall be used to indicate that faces are to be excluded without falling back on any other geometry. Such designation could be used for portions of a site beneath a building or other structure.

The flag Hole shall be used to indicate that faces are to be excluded but may fall back on other geometry. Such designation could be used for portions of a proposed site that are to remain unchanged (conforming to an existing site that may also be defined)

For scenarios where multiple surfaces used as input are to be combined, any triangles marked Void shall be retained as voids, while any triangles marked as Hole shall be overridden if another surface has visible geometry defined within the same horizontal location.

8.8.3.48.2 Entity inheritance

8.8.3.48.3 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. 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.
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. `3` The space dimensionality of this geometric representation item, it is always 3.
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). NOTE 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. `SIZEOF(CoordIndex)` Derived number of triangles used for this triangulation.
Click to show 11 hidden inherited attributes
IfcTriangulatedIrregularNetwork (1)
6	Flags	LIST [1:?] OF IfcInteger	Indicates attributes of each triangle in a compact form as follows: -2 = invisible void; -1 = invisible hole; 0 = no breaklines; 1 = breakline at edge 1; 2 = breakline at edge 2; 3 = breakline at edges 1 and 2; 4 = breakline at edge 3; 5 = breakline at edges 1 and 3; 6 = breakline at edges 2 and 3; 7 = breakline at edges 1, 2, and 3.

Table 8.8.3.48.A

8.8.3.48.4 Formal propositions

Name	Description
NotClosed	The triangulated face set shall not be closed.
`SELF\IfcTriangulatedFaceSet.Closed = FALSE`

Table 8.8.3.48.B

8.8.3.48.5 Formal representation

 ENTITY IfcTriangulatedIrregularNetwork
 SUBTYPE OF (IfcTriangulatedFaceSet);
	Flags : LIST [1:?] OF IfcInteger;
 WHERE
	NotClosed : SELF\IfcTriangulatedFaceSet.Closed = FALSE;
END_ENTITY;

8.8.3.48.6 References

IfcTriangulatedFaceSet