8.9.3.19 IfcClothoid
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.
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.
8.9.3.19.2 Entity inheritance
-
- IfcCurve
- IfcAnnotationFillArea
- IfcBooleanResult
- IfcBoundingBox
- IfcCartesianPointList
- IfcCartesianTransformationOperator
- IfcCsgPrimitive3D
- IfcDirection
- IfcFaceBasedSurfaceModel
- IfcFillAreaStyleHatching
- IfcFillAreaStyleTiles
- IfcGeometricSet
- IfcHalfSpaceSolid
- IfcLightSource
- IfcPlacement
- IfcPlanarExtent
- IfcPoint
- IfcSectionedSpine
- IfcSegment
- IfcShellBasedSurfaceModel
- IfcSolidModel
- IfcSurface
- IfcTessellatedItem
- IfcTextLiteral
- IfcVector
8.9.3.19.3 Attributes
| # | 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. |
|
| 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. |
|
| IfcCurve (1) | |||
| * | Dim | IfcDimensionCount |
This attribute is formally derived. 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. |
8.9.3.19.4 Examples
8.9.3.19.5 Formal representation
ENTITY IfcClothoid
SUBTYPE OF (IfcSpiral);
ClothoidConstant : IfcLengthMeasure;
END_ENTITY;