IfcEdgeLoop

注：定义根据ISO/CD 10303-42:1992

边环是一个非零范围的环。这是一条起点和终点相同的路径。它的域（如果存在的话）是一条闭合曲线。边缘环可能会重叠。

注：实体改编自ISO 10303-42中定义的边缘环。

IFC2x2中增加的新实体。

非正式提议：

①IfcEdgeLoop的属应为1或更大。

②应满足欧拉公式：（顶点数）+亏格-（边数）=1；

③同一个具有相同意义的IfcEdgeLoop不能多次引用任何边。为此，非定向边的边被视为具有真实意义的引用。

Formal Propositions

Rule	Description
IsClosed	The start vertex of the first edge shall be the same as the end vertex of the last edge. This ensures that the path is closed to form a loop.
IsContinuous	The end vertex of each edge shall be the same as the start vertex of its successor.

 

#	Attribute	Type	Cardinality	Description	C
IfcRepresentationItem
	LayerAssignment	IfcPresentationLayerAssignment @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.	X
	StyledByItem	IfcStyledItem @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.	X
IfcTopologicalRepresentationItem
IfcLoop
IfcEdgeLoop
1	EdgeList	IfcOrientedEdge	L[1:?]	A list of oriented edge entities which are concatenated together to form this path.	X
	Ne :=SIZEOF(EdgeList)	IfcInteger	[1:1]	The number of elements in the edge list.	X

 

EXPRESS Specification

ENTITY IfcEdgeLoop
 SUBTYPE OF (IfcLoop);
  EdgeList : LIST [1:?] OF IfcOrientedEdge;
 DERIVE
  Ne : IfcInteger := SIZEOF(EdgeList);
 WHERE
  IsClosed : (EdgeList[1].EdgeStart) :=: (EdgeList[Ne].EdgeEnd);
  IsContinuous : IfcLoopHeadToTail(SELF);
END_ENTITY;