8.9.3.18 IfcCompositeCurve

Courbe composite
Zusammengesetzte Kurve

An IfcCompositeCurve is a continuous curve composed of curve segments.

Figure 317 illustrates an example of a composite curve.

formula

Figure 317 — Composite curve

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

The arch should be parameterized:

Then the parameterization of the composite curve is:

 

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 ith segment is parameterized from:

formula

where lk is the parametric length (i.e., difference between maximum and minimum parameter values) of the curve underlying the kth 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 ti; ti0 ti ti1; for the ith segment by the equation:

formula if Segments[i].SameSense = TRUE;

or by the equation:

formula if Segments[i].SameSense = FALSE;

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

formula 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:

  1. 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.

Figure 318 illustrates composite curve usage.

usage

Figure 318 — Composite curve usage

XSD 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:logical" use="optional"/>
   </xs:extension>
  </xs:complexContent>
 </xs:complexType>

EXPRESS Specification:

ENTITY IfcCompositeCurve
SUPERTYPE OF(IfcCompositeCurveOnSurface)
SUBTYPE OF IfcBoundedCurve;
Segments : LIST [1:?] OF IfcCompositeCurveSegment;
SelfIntersect : LOGICAL;
DERIVE
NSegments : INTEGER := SIZEOF(Segments);
ClosedCurve : LOGICAL := 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;

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

Segments : 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.
SelfIntersect : Indication of whether the curve intersects itself or not; this is for information only.
NSegments : The number of component curves.
ClosedCurve : Indication whether the curve is closed or not; this is derived from the transition code of the last segment.

Formal Propositions:

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.

Inheritance Graph:

ENTITY IfcCompositeCurve
ENTITY IfcRepresentationItem
INVERSE
LayerAssignment : SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem : SET [0:1] OF IfcStyledItem FOR Item;
ENTITY IfcGeometricRepresentationItem
ENTITY IfcCurve
DERIVE
Dim : IfcDimensionCount := IfcCurveDim(SELF);
ENTITY IfcBoundedCurve
ENTITY IfcCompositeCurve
Segments : LIST [1:?] OF IfcCompositeCurveSegment;
SelfIntersect : LOGICAL;
DERIVE
NSegments : INTEGER := SIZEOF(Segments);
ClosedCurve : LOGICAL := Segments[NSegments].Transition <> Discontinuous;
END_ENTITY;

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