IfcCompositeCurve

Semantic definitions at the entity

Entity definition

An IfcCompositeCurve is a continuous curve composed of curve segments.

Figure 368 illustrates an example of a composite curve.

Figure 368 — Composite curve

Consider an IfcCompositeCurve having line segment and an arc segment. The line should be parameterized:

IfcPolyline with start= 0.,0. end= 0.,1., SameSense= TRUE, parametric length = 1.

The arch should be parameterized:

IfcTrimmedCurve with start= 180', end= 90', SameSense= FALSE, parametric length = 90.

Then the parameterization of the composite curve is:

IfcCompositeCurve with 0. ≤ T ≤ 1. (line segment) and 1. ≤ T ≤ 91. (arc segment), parametric length = 91.

NOTE Definition according to ISO 10303-42:
A composite curve is a collection of curves joined end-to-end. The individual segments of the curve are themselves defined as composite curve segments. The parameterization of the composite curve is an accumulation of the parametric ranges of the referenced bounded curves. The first segment is parameterized from 0 to l₁ and for i ≤ 2, the i^th segment is parameterized from:

where l_k is the parametric length (i.e., difference between maximum and minimum parameter values) of the curve underlying the k^th segment. Let T denote the parameter for the composite curve. Then, if the ith segment is not a reparameterised composite curve segment, T is related to the parameter t_i; t_i0 ≤ t_i ≤ t_i1; for the ith segment by the equation:

if Segments[i].SameSense = TRUE;

or by the equation:

if Segments[i].SameSense = FALSE;

If the segments[i] is of type reparameterised composite curve segment,

where τ is defined at reparameterized composite curve segment (see IfcReparameterizedCompositeCurveSegment).

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

HISTORY New entity in IFC1.0

Informal Propositions:

The SameSense attribute of each segment correctly specifies the senses of the component curves. When traversed in the direction indicated by SameSense, the segments shall join end-to-end.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
1	Segments	IfcCompositeCurveSegment	L[1:?]	The component bounded curves, their transitions and senses. The transition attribute for the last segment defines the transition between the end of the last segment and the start of the first; this transition attribute may take the value discontinuous, which indicates an open curve.	X
2	SelfIntersect	IfcLogical		Indication of whether the curve intersects itself or not; this is for information only.	X
	NSegments :=SIZEOF(Segments)	IfcInteger		The number of component curves.	X
	ClosedCurve :=Segments[NSegments].Transition <> Discontinuous	IfcLogical		Indication whether the curve is closed or not; this is derived from the transition code of the last segment.	X

Formal Propositions

Rule	Description
CurveContinuous	No transition code should be Discontinuous, except for the last code of an open curve.
SameDim	Ensures, that all segments used in the curve have the same dimensionality.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
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. 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.	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. IFC2x3 CHANGE The inverse attribute StyledByItem has been added.	X
IfcGeometricRepresentationItem
IfcCurve
	Dim :=IfcCurveDim(SELF)	IfcDimensionCount		The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.	X
IfcBoundedCurve
IfcCompositeCurve
1	Segments	IfcCompositeCurveSegment	L[1:?]	The component bounded curves, their transitions and senses. The transition attribute for the last segment defines the transition between the end of the last segment and the start of the first; this transition attribute may take the value discontinuous, which indicates an open curve.	X
2	SelfIntersect	IfcLogical		Indication of whether the curve intersects itself or not; this is for information only.	X
	NSegments :=SIZEOF(Segments)	IfcInteger		The number of component curves.	X
	ClosedCurve :=Segments[NSegments].Transition <> Discontinuous	IfcLogical		Indication whether the curve is closed or not; this is derived from the transition code of the last segment.	X

Formal representations

XML Specification

 <xs:element name="IfcCompositeCurve" type="ifc:IfcCompositeCurve" substitutionGroup="ifc:IfcBoundedCurve" nillable="true"/>

 <xs:complexType name="IfcCompositeCurve">

  <xs:complexContent>

   <xs:extension base="ifc:IfcBoundedCurve">

    <xs:sequence>

     <xs:element name="Segments">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcCompositeCurveSegment" maxOccurs="unbounded"/>

       </xs:sequence>

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

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

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

      </xs:complexType>

     </xs:element>

    </xs:sequence>

    <xs:attribute name="SelfIntersect" type="ifc:IfcLogical" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcCompositeCurve

 SUPERTYPE OF(IfcCompositeCurveOnSurface)

 SUBTYPE OF (IfcBoundedCurve);

  Segments : LIST [1:?] OF IfcCompositeCurveSegment;

  SelfIntersect : IfcLogical;

 DERIVE

  NSegments : IfcInteger := SIZEOF(Segments);

  ClosedCurve : IfcLogical := Segments[NSegments].Transition <> Discontinuous;

 WHERE

  CurveContinuous : ((NOT ClosedCurve) AND (SIZEOF(QUERY(Temp <* Segments | Temp.Transition = Discontinuous)) = 1)) OR ((ClosedCurve) AND (SIZEOF(QUERY(Temp <* Segments | Temp.Transition = Discontinuous)) = 0));
  SameDim : SIZEOF( QUERY( Temp <* Segments | Temp.Dim <> Segments[1].Dim)) = 0;
END_ENTITY;

 EXPRESS-G diagram

	Zusammengesetzte Kurve
	Composite Curve
	Courbe composite

Item	Change	Description
IFC4 Addendum 1
IfcCompositeCurve
SelfIntersect	MODIFIED	Type changed from LOGICAL to IfcLogical.