| Item | SPF | XML | Change | Description | IFC4x3_RC1 to IFC4x3_RC2 |
|---|---|---|---|---|
| IfcClothoid | ADDED | IFC4x3_RC2 to IFC4x3_RC3 | ||
| IfcClothoid | ||||
| Position | MODIFIED | Instantiation changed to OPTIONAL. |
A clothoid is a planar curve in the form of a spiral. This curve has the property that the curvature varies linearly with the arc length.
NOTE Definition according to ISO 10303-42:2003
Interpretation of the data shall be as follows:
C = SELF\IfcSpiral.Position.Location x = SELF\IfcSpiral.Position.P[1] y = SELF\IfcSpiral.Position.P[2] A = ClothoidConstantand the clothoid is parameterized as:
and the parametric range is: -∞ < u < ∞
The arc length s of the curve, from the point C, is given by the formula:
The curvature κ and radius of the curvature ρ, at any point of the curve, are related to the arc length s by the formulae:
NOTE Formulae adapted from clothoid defined in ISO 10303-42
| # | Attribute | Type | Cardinality | Description | G |
|---|---|---|---|---|---|
| 2 | ClothoidConstant | IfcLengthMeasure | The constant which defines the relationship between curvature and arc length for the curve. | X |
| # | 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 | ||
| IfcSpiral | |||||
| 1 | Position | IfcAxis2Placement | X | ||
| IfcClothoid | |||||
| 2 | ClothoidConstant | IfcLengthMeasure | The constant which defines the relationship between curvature and arc length for the curve. | X | |
<xs:element name="IfcClothoid" type="ifc:IfcClothoid" substitutionGroup="ifc:IfcSpiral" nillable="true"/>
<xs:complexType name="IfcClothoid">
<xs:complexContent>
<xs:extension base="ifc:IfcSpiral">
<xs:attribute name="ClothoidConstant" type="ifc:IfcLengthMeasure" use="optional"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
ENTITY IfcClothoid
SUBTYPE OF (IfcSpiral);
ClothoidConstant : IfcLengthMeasure;
END_ENTITY;
EXPRESS-G diagram
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