IFC 4.3.x development

8.20.3.15 IfcPolyLoop

Change log

IFC4

additionswhere_rulesAllPointsSameDim
deletionswhere_rulesWR21

IFC4X2

modificationsattributes Polygon definitionChanged from list[3:?] of unique IfcCartesianPoint to list[3:?] of IfcCartesianPoint

IFC4X3_RC3

modificationsattributes Polygon definitionChanged from list[3:?] of IfcCartesianPoint to list[3:?] of unique IfcCartesianPoint

8.20.3.15.1 Semantic definitions at the entity

NOTE  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 Image

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.

NOTE  This entity exists primarily to facilitate the efficient communication of faceted B-rep models.

 

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

HISTORY   New entity in IFC1.0

Informal Propositions:

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

8.20.3.15.1 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
IfcLoop
IfcPolyLoop
1 Polygon LIST [3:?] OF UNIQUE IfcCartesianPoint List of points defining the loop. There are no repeated points in the list.

8.20.3.15.2 Entity inheritance

dot_inheritance IfcPolyLoop IfcPolyLoop IfcLoop IfcLoop IfcPolyLoop->IfcLoop IfcEdgeLoop IfcEdgeLoop IfcEdgeLoop->IfcLoop IfcTopologicalRepresentationItem IfcTopologicalRepresentationItem IfcLoop->IfcTopologicalRepresentationItem IfcVertexLoop IfcVertexLoop IfcVertexLoop->IfcLoop IfcTopologicalRepresentationItem_children 6 more... IfcTopologicalRepresentationItem_children->IfcTopologicalRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcTopologicalRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.20.3.15.3 Formal representations

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;