NOTE Definition according to ISO/CD 10303-42:1992

A loop is a topological entity constructed from a single vertex, or by stringing together connected (oriented) edges, or linear segments beginning and ending at the same vertex. It is typically used to bound a face lying on a surface. A loop has dimensionality of 0 or 1. The domain of a 0-dimensional loop is a single point. The domain of a 1-dimensional loop is a connected, oriented curve, but need not to be manifold. As the loop is a circle, the location of its beginning/ending point is arbitrary. The domain of the loop includes its bounds, an 0 ≤ Ξ < ∞. A loop is represented by a single vertex, or by an ordered collection of oriented edges, or by an ordered collection of points. A loop is a graph, soMand the graph genusG^l^may be determined by the graph traversal algorithm. SinceM= 1, the Euler equation (1) reduces in this case towhere

VandE~l~are the number of unique vertices and oriented edges in the loop andG^l^is the genus of the loop.NOTE Entity adapted from

loopdefined in ISO 10303-42.HISTORY New entity in IFC2x.

Informal Propositions:

- A loop has a finite extent.
- A loop describes a closed (topological) curve with coincident start and end vertices.

# | Attribute | Type | Description |
---|---|---|---|

IfcRepresentationItem | |||

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. |

ENTITY IfcLoop SUPERTYPE OF (ONEOF (IfcEdgeLoop ,IfcPolyLoop ,IfcVertexLoop)) SUBTYPE OF (IfcTopologicalRepresentationItem); END_ENTITY;