IfcLoop

BACnet MVD

#### IfcLoop

Natural language names

| Schleife - Topologie
| Loop
| Boucle

##### Semantic definitions at the entity

Entity definition

> 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, so M and the graph genus Gl may be determined by the graph traversal algorithm. Since M = 1, the Euler equation (1) reduces in this case to

> where V and El are the number of unique vertices and oriented edges in the loop and Gl is the genus of the loop.

> NOTE Entity adapted from loop defined in ISO 10303-42.

> HISTORY New entity in IFC2x.

Informal Propositions:

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

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
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.

> 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.

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.

> IFC2x3 CHANGE The inverse attribute StyledByItem has been added.

X

X

IfcTopologicalRepresentationItem
IfcLoop

##### Formal representations

XML Specification
`<xs:element name="IfcLoop" type="ifc:IfcLoop" substitutionGroup="ifc:IfcTopologicalRepresentationItem" nillable="true"/>
<xs:complexType name="IfcLoop">
<xs:complexContent>
<xs:extension base="ifc:IfcTopologicalRepresentationItem"/>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`ENTITY IfcLoop
SUPERTYPE OF(ONEOF(IfcEdgeLoop, IfcPolyLoop, IfcVertexLoop))
SUBTYPE OF (IfcTopologicalRepresentationItem);
END_ENTITY;

EXPRESS-G diagram

`

References: IfcFaceBound

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