IfcLoop

Definition from 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 G^l may be determined by the graph traversal algorithm. Since M = 1, the Euler equation (1) reduces in this case to

where V and E_l are the number of unique vertices and oriented edges in the loop and G^l is the genus of the loop.

NOTE: Corresponding STEP entity: loop, the following subtypes have been incorporated into IFC: poly_loop as IfcPolyLoop, vertex_loop as IfcVertexLoop, edge_loop as IfcEdgeLoop. Please refer to ISO/IS 10303-42:1994, p. 136 for the final definition of the formal standard.

HISTORY: New Entity in IFC Release 2.x.

Informal propositions:

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

EXPRESS specification:

ENTITY IfcLoop

SUPERTYPE OF

(ONEOF(IfcPolyLoop, IfcVertexLoop, IfcEdgeLoop))

SUBTYPE OF (

IfcTopologicalRepresentationItem);

END_ENTITY;

Inheritance graph

ENTITY IfcLoop;

ENTITY IfcRepresentationItem;

INVERSE

LayerAssignments

SET OF IfcPresentationLayerAssignment FOR AssignedItems;

StyledByItem

SET [0:1] OF IfcStyledItem FOR Item;

ENTITY IfcTopologicalRepresentationItem;

ENTITY IfcLoop;

END_ENTITY;