8.20.3.15 IfcPolyLoop

Definition according to ISO/CD 10303-42:1992 A poly loop is a loop with straight edges bounding a planar region in space. A poly loop is a loop of genus 1 where the loop is represented by an ordered coplanar collection of points forming the vertices of the loop. The loop is composed of straight line segments joining a point in the collection to the succeeding point in the collection. The closing segment is from the last to the first point in the collection. The direction of the loop is in the direction of the line segments.

A poly loop shall conform to the following topological constraints: > * the loop has the genus of one. * the following equation shall be satisfied
Figure 8.20.3.15.A

The IfcPolyLoop is always closed and the last segment is from the last IfcCartesianPoint in the list of Polygon's to the first IfcCartesianPoint. Therefore the first point shall not be repeated at the end of the list, neither by referencing the same instance, nor by using an additional instance of IfcCartesianPoint having the coordinates as the first point.

This entity exists primarily to facilitate the efficient communication of faceted B-rep models. Entity adapted from poly_loop defined in ISO 10303-42. New entity in IFC1.0

Informal Propositions

All the points in the polygon defining the poly loop shall be coplanar.
The first and the last Polygon shall be different by value.

8.20.3.15.2 Entity inheritance

8.20.3.15.3 Attributes

#	Attribute	Type	Description
IfcRepresentationItem (2)
	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.
Click to show 2 hidden inherited attributes Click to hide 2 inherited attributes
IfcPolyLoop (1)
1	Polygon	LIST [3:?] OF UNIQUE IfcCartesianPoint	List of points defining the loop. There are no repeated points in the list.

Table 8.20.3.15.E

8.20.3.15.4 Formal propositions

Name	Description
AllPointsSameDim	The space dimensionality of all Points shall be the same.
`SIZEOF(QUERY(Temp <* Polygon \| Temp.Dim <> Polygon[1].Dim)) = 0`

Table 8.20.3.15.F

8.20.3.15.5 Examples

Figure 8.20.3.15.B

Surface Model
Figure 8.20.3.15.C

Basin Faceted Brep
Figure 8.20.3.15.D

Brep Model

8.20.3.15.6 Formal representation

ENTITY IfcPolyLoop
 SUBTYPE OF (IfcLoop);
	Polygon : LIST [3:?] OF UNIQUE IfcCartesianPoint;
 WHERE
	AllPointsSameDim : SIZEOF(QUERY(Temp <* Polygon | Temp.Dim <> Polygon[1].Dim)) = 0;
END_ENTITY;

8.20.3.15.7 References

IfcLoop

8.20.3.15 IfcPolyLoop

8.20.3.15.1 Semantic definition

8.20.3.15.2 Entity inheritance

8.20.3.15.3 Attributes

8.20.3.15.4 Formal propositions

8.20.3.15.5 Examples

8.20.3.15.6 Formal representation

8.20.3.15.7 References

8.20.3.15.8 Changelog

8.20.3.15.8.1 IFC4

8.20.3.15.8.2 IFC4.2

8.20.3.15.8.3 IFC4.3_DEV_33fdbb94