8.9.3.19 IfcClothoid

AbV ⓘ

8.9.3.19.1 Semantic definition

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.

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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 = ClothoidConstant

The clothoid is parameterized as:

$$\lambda(u)=C+A\sqrt{\pi}(\int_{0}^{u}\cos(\pi\frac{At^2}{2|A|})dt\ x+\int_{0}^{u}\sin(\pi\frac{At^2}{2|A|})dt\ y)$$

The parametric range is: -∞ < u < ∞

The arc length s of the curve, from the point C, is given by the formula:

$$s=Au\sqrt{\pi}$$

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:

$$\kappa=\frac{As}{|A^3|}, \rho=\frac{1}{\kappa}$$

The constant A, known as flatness or homothetic parameter of the clothoid, is specified as:

$$ A=\sqrt{LR}$$

where, L is the length measured from the inflection point; and R is the radius of the clothoid.

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#	Attribute	Type	Description
IfcRepresentationItem (2)
	LayerAssignment	SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems	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.
	StyledByItem	SET [0:1] OF IfcStyledItem FOR Item	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.
IfcCurve (1)
*	Dim	IfcDimensionCount	This attribute is formally derived. `IfcCurveDim(SELF)` The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.
IfcSpiral (1)
1	Position	IfcAxis2Placement	No description available.
Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcClothoid (1)
2	ClothoidConstant	IfcLengthMeasure	The constant which defines the relationship between curvature and arc length for the curve.

Table A

ENTITY IfcClothoid
SUBTYPE OF (IfcSpiral);
ClothoidConstant : IfcLengthMeasure;
END_ENTITY;