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.
Definition according to ISO 10303-42:2003Interpretation 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: -â < u < â
The arc length s of the curve, from the point C, is given by the formula:
$$s=Au\sqrt{\pi}$$
The curvature Îș and radius of the curvature Ï, 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.
Formulae adapted from clothoid defined in ISO 10303-428.9.3.19.2 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. The inverse attribute LayerAssignments has been added. 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. The inverse attribute StyledByItem has been added. |
|
| 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;