注：定义根据ISO/CD 10303-42:1992
顶点环是由一个顶点构成的零亏格环。顶点可以独立于顶点循环而存在。拓扑数据应满足以下约束：
注：实体改编自ISO 10303-42中定义的顶点环。
IFC2x2中的历史新实体。
非正式提议：
①顶点循环的范围和维数为零。
②顶点循环具有亏格0。
| # | 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 | |||||
| IfcVertexLoop | |||||
| 1 | LoopVertex | IfcVertex | [1:1] | The vertex which defines the entire loop. | X |
EXPRESS Specification
ENTITY IfcVertexLoop
SUBTYPE OF (IfcLoop);
LoopVertex : IfcVertex;
END_ENTITY;
原文：https://www.cnblogs.com/herd/p/14090606.html