8.20.3.4 IfcEdge

8.20.3.4.1 Semantic definition

An IfcEdge defines two vertices being connected topologically. The geometric representation of the connection between the two vertices defaults to a straight line if no curve geometry is assigned using the subtype IfcEdgeCurve. The IfcEdge can therefore be used to exchange straight edges without an associated geometry provided by IfcLine or IfcPolyline thought IfcEdgeCurve.EdgeGeometry.

edge representation — Figure 8.20.3.4.A — Edge representation

NOTE Definition according to ISO/CD 10303-42:1992 An edge is the topological construct corresponding to the connection of two vertices. More abstractly, it may stand for a logical relationship between two vertices. The domain of an edge, if present, is a finite, non-self-intersecting open curve in R^M^, that is, a connected 1-dimensional manifold. The bounds of an edge are two vertices, which need not be distinct. The edge is oriented by choosing its traversal direction to run from the first to the second vertex. If the two vertices are the same, the edge is a self loop. The domain of the edge does not include its bounds, and 0 ≤ Ξ ≤ ∞. Associated with an edge may be a geometric curve to locate the edge in a coordinate space; this is represented by the edge curve subtype. The curve shall be finite and non-self-intersecting within the domain of the edge. An edge is a graph, so its multiplicity M and graph genus G^e^ may be determined by the graph traversal algorithm. Since M = E = 1, the Euler equation (1) reduces in the case to:

where V = 1 or 2, and G^e^ = 1 or 0. Specifically, the topological edge defining data shall satisfy: > * an edge has two vertices * the vertices need not be distinct * Equation shall hold
Figure 8.20.3.4.B
Figure 8.20.3.4.C
Figure 8.20.3.4.D
Figure 8.20.3.4.E

Informal Propositions

The edge has dimensionality 1.
The extent of an edge shall be finite and nonzero.

8.20.3.4.2 Entity inheritance

8.20.3.4.3 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.
Click to show 2 hidden inherited attributes
IfcEdge (2)
1	EdgeStart	IfcVertex	Start point (vertex) of the edge.
2	EdgeEnd	IfcVertex	End point (vertex) of the edge. The same vertex can be used for both EdgeStart and EdgeEnd.

Table 8.20.3.4.G

8.20.3.4.4 Examples

Figure 8.20.3.4.F

Structural Curve Member

8.20.3.4.5 Formal representation

 ENTITY IfcEdge
 SUPERTYPE OF (ONEOF
	(IfcEdgeCurve
	,IfcOrientedEdge
	,IfcSubedge))
 SUBTYPE OF (IfcTopologicalRepresentationItem);
	EdgeStart : IfcVertex;
	EdgeEnd : IfcVertex;
END_ENTITY;