#### 8.17.3.5 IfcLoop

| Boucle
| Schleife - Topologie

> 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.

XSD 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

| SUBTYPE OF (IfcTopologicalRepresentationItem);

END_ENTITY;

Inheritance Graph:

ENTITY IfcLoop

| ENTITY IfcRepresentationItem

| INVERSE

LayerAssignment | : | SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem | : | SET [0:1] OF IfcStyledItem FOR Item;

| ENTITY IfcTopologicalRepresentationItem

| ENTITY IfcLoop

END_ENTITY;

Link to this page