IFC 4.3.0.1 (IFC4X3) development

8.9.3.74 IfcToroidalSurface

8.9.3.74.1 Semantic definition

The IfcToroidalSurface is a bounded elementary surface. It is constructed by completely revolving a circle around an axis line. The inherited Position attribute defines the IfcAxisPlacement3D and provides:

σ(u,v) = C + (R + r_cos _v)((cos_u_)x + (sin u))y) + r(sin_v_))z

where the parametrisation range is 0 ≤ u, v ≤ 360 degrees. u and v are angular parameters and when numerical values are specified they shall use the current units for plane angle measure.

In the placement coordinate system defined above, the surface is represented by the equation S = 0, where

S(x, y, z) = x^2^ + y^2^ + z^2^ -2R√(x^2^+y^2^) - r^2^ + R^2^.

The positive direction of the normal to the surface at any point on the surface is given by

( S~x~, S~y~, S~z~ ).

The unit normal is given by

N(u,v) = cos_v_((cos u)x + (sin u)y) + (sin v)z.

The sense of this normal is away from the nearest point on the circle of radius R with centre C. A manifold surface will be produced if the major radius is greater than the minor radius. If this condition is not fulfilled, the resulting surface will be self-intersecting.

8.9.3.74.2 Entity inheritance

8.9.3.74.3 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.

IfcSurface (1)
* Dim IfcDimensionCount

This attribute is formally derived.

3

The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.

IfcElementarySurface (1)
1 Position IfcAxis2Placement3D

The position and orientation of the surface. This attribute is used in the definition of the parameterization of the surface.

Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcToroidalSurface (2)
2 MajorRadius IfcPositiveLengthMeasure

The major radius of the torus.

3 MinorRadius IfcPositiveLengthMeasure

The minor radius of the torus.

Table 8.9.3.74.A

8.9.3.74.4 Formal propositions

Name Description
MajorLargerMinor

The attribute value of the MinorRadius shall be smaller then the value of the MajorRadius

MinorRadius < MajorRadius
Table 8.9.3.74.B

8.9.3.74.5 Formal representation

ENTITY IfcToroidalSurface
 SUBTYPE OF (IfcElementarySurface);
	MajorRadius : IfcPositiveLengthMeasure;
	MinorRadius : IfcPositiveLengthMeasure;
 WHERE
	MajorLargerMinor : MinorRadius < MajorRadius;
END_ENTITY;

8.9.3.74.6 References

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8.9.3.74.7 Changelog

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