Natural language names
Polygonale Schleife - Topologie
Poly Loop
Semantic definitions at the entity
Entity definition

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
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.
Attribute definitions
#AttributeTypeCardinalityDescription G
1PolygonIfcCartesianPointL[3:?] List of points defining the loop. There are no repeated points in the list. X
Formal Propositions
AllPointsSameDimThe space dimensionality of all Points shall be the same.
Inherited definitions from supertypes
Entity inheritance IfcLoop IfcTopologicalRepresentationItem IfcRepresentationItem
Attribute inheritance
S[0:1]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.
S[0:1]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.
1PolygonIfcCartesianPointL[3:?] List of points defining the loop. There are no repeated points in the list. X
Formal representations
XML Specification
 <xs:element name="IfcPolyLoop" type="ifc:IfcPolyLoop" substitutionGroup="ifc:IfcLoop" nillable="true"/>
 <xs:complexType name="IfcPolyLoop">
   <xs:extension base="ifc:IfcLoop">
     <xs:element name="Polygon">
        <xs:element ref="ifc:IfcCartesianPoint" minOccurs="3" maxOccurs="unbounded"/>
       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcCartesianPoint"/>
       <xs:attribute ref="ifc:cType" fixed="list-unique"/>
       <xs:attribute ref="ifc:arraySize" use="optional"/>
EXPRESS Specification
ENTITY IfcPolyLoop
 SUBTYPE OF (IfcLoop);
  Polygon : LIST [3:?] OF UNIQUE IfcCartesianPoint;
  AllPointsSameDim : SIZEOF(QUERY(Temp <* Polygon | Temp.Dim <> Polygon[1].Dim)) = 0;

Link to EXPRESS-G diagram EXPRESS-G diagram

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