IfcPolyLoop

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:

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

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
1	Polygon	IfcCartesianPoint	~L[3:?]	List of points defining the loop. There are no repeated points in the list.	X

Formal Propositions

Rule	Description
AllPointsSameDim	The space dimensionality of all Points shall be the same.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcRepresentationItem
	LayerAssignment	IfcPresentationLayerAssignment @AssignedItems	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.	X
	StyledByItem	IfcStyledItem @Item	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.	X
IfcTopologicalRepresentationItem
IfcLoop
IfcPolyLoop
1	Polygon	IfcCartesianPoint	~L[3:?]	List of points defining the loop. There are no repeated points in the list.	X

Formal representations

XSD Specification

 <xs:element name="IfcPolyLoop" type="ifc:IfcPolyLoop" substitutionGroup="ifc:IfcLoop" nillable="true"/>

 <xs:complexType name="IfcPolyLoop">

  <xs:complexContent>

   <xs:extension base="ifc:IfcLoop">

    <xs:sequence>

     <xs:element name="Polygon">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcCartesianPoint" minOccurs="3" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcCartesianPoint"/>

       <xs:attribute ref="ifc:cType" fixed="list-unique"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

    </xs:sequence>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


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;

 EXPRESS-G diagram

	Polygonale Schleife - Topologie
	Poly Loop