IFC 4.3.x development

8.20.3.13 IfcOrientedEdge

Change log

IFC4

additions where_rules EdgeElementNotOriented
deletions where_rules WR1
modificationsattributes Orientation definitionChanged from boolean to IfcBoolean

IFC4X1

additionswhere_rulesEdgeElementNotOriented
deletionswhere_rulesEdgeElementNotOriented

IFC4X2

additionswhere_rulesEdgeElementNotOriented
deletionswhere_rulesEdgeElementNotOriented

IFC4X3_RC3

additionswhere_rulesEdgeElementNotOriented
deletionswhere_rulesEdgeElementNotOriented

8.20.3.13.1 Semantic definitions at the entity

The IfcOrientedEdge represents an IfcEdge with an Orientation flag applied. It allows to reuse the same IfcEdge when traversed exactly twice, once forwards and once backwards.

NOTE  The sense of the normal to the IfcFace is solely determined from the edges. If all the edges of the face are connected in a counter clockwise manner following the edge orientations the face normal will point outward. The normal to the underlying IfcFaceSurface representing the geometry of that face has no relevance to this. The purpose of the IfcFaceSurface.SameSense attribute is to give additional information for verification purposes. SameSense TRUE means surface normal and face normal are the same, SameSense FALSE means they are in opposite directions.

The reused edge with a geometric representation as IfcEdgeCurve defines the edge in 3D coordinate space. In some cases, particularly when using elementary or swept surfaces, there is the risk of imprecise mapping of the 3D (x, y, z) IfcEdgeCurve onto the adjacent surfaces to determine the boundaries of these surfaces. The optional CurveOnSurface defines the 2D (u, v) edge within the parametric space of the surface. It could be used to determine the correctness of the mapping of the 3D IfcEdgeCurve onto this surface.


example
EXAMPLE  Figure 1 illustrates an example where the CurveOnSurface is provided in addition to the curve geometry of the IfcEdgeCurve.

Figure 1 — Curve on surface representation of an IfcOrientedEdge

  

NOTE  Definition according to ISO/CD 10303-42:1992
An oriented edge is an edge constructed from another edge and contains a BOOLEAN direction flag to indicate whether or not the orientation of the constructed edge agrees with the orientation of the original edge. Except for perhaps orientation, the oriented edge is equivalent to the original edge.

A common practice is solid modelling systems is to have an entity that represents the "use" or "traversal" of an edge. This "use" entity explicitly represents the requirement in a manifold solid that each edge must be traversed exactly twice, once in each direction. The "use" functionality is provided by the edge subtype oriented edge.

NOTE  Entity adapted from oriented_edge defined in ISO 10303-42.

HISTORY  New entity in IFC2.0.

IFC4 Add2 CHANGE  The attribute CurveOnSurface has been added.

8.20.3.13.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignmentSET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment 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.
IfcTopologicalRepresentationItem
IfcEdge
1 EdgeStart IfcVertex Start point (vertex) of the edge.
2 EdgeEnd IfcVertex End point (vertex) of the edge. The same vertex can be used for both EdgeStart and EdgeEnd.
IfcOrientedEdge
3 EdgeElement IfcEdge Edge entity used to construct this oriented edge.
4 Orientation IfcBoolean BOOLEAN, If TRUE the topological orientation as used coincides with the orientation from start vertex to end vertex of the edge element. If FALSE otherwise.
1 EdgeStart INVALID The start vertex of the oriented edge. It derives from the vertices of the edge element after taking account of the orientation.
2 EdgeEnd INVALID The end vertex of the oriented edge. It derives from the vertices of the edge element after taking account of the orientation.

8.20.3.13.2 Entity inheritance

dot_inheritance IfcOrientedEdge IfcOrientedEdge IfcEdge IfcEdge IfcOrientedEdge->IfcEdge IfcEdgeCurve IfcEdgeCurve IfcEdgeCurve->IfcEdge IfcTopologicalRepresentationItem IfcTopologicalRepresentationItem IfcEdge->IfcTopologicalRepresentationItem IfcSubedge IfcSubedge IfcSubedge->IfcEdge IfcTopologicalRepresentationItem_children 6 more... IfcTopologicalRepresentationItem_children->IfcTopologicalRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcTopologicalRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.20.3.13.3 Formal representations

ENTITY IfcOrientedEdge
 SUBTYPE OF (IfcEdge);
	EdgeElement : IfcEdge;
	Orientation : IfcBoolean;
 DERIVE
	 SELF\IfcEdge.EdgeStart : IfcVertex := IfcBooleanChoose 
(Orientation, EdgeElement.EdgeStart, EdgeElement.EdgeEnd);
	 SELF\IfcEdge.EdgeEnd : IfcVertex := IfcBooleanChoose 
(Orientation, EdgeElement.EdgeEnd, EdgeElement.EdgeStart);
 WHERE
	EdgeElementNotOriented : NOT('IFC4X3_DEV_a1492713.IFCORIENTEDEDGE' IN TYPEOF(EdgeElement));
END_ENTITY;