IfcToroidalSurface

Item	SPF	XML	Change	Description
IFC4 Addendum 2
IfcToroidalSurface			ADDED

Semantic definitions at the entity

Entity 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:

SELF\IfcElementarySurface.Position: The location and orientation of the axis system for the primitive.
SELF\IfcElementarySurface.Position.Location: The center of the toroidal surface.
SELF\IfcElementarySurface.Position.Position[3]: The axis of revolution of the toroidal surface

NOTE Definition according to ISO/CD 10303-42:1992

An IfcToroidalSurface is a type of elementary surface, which could be produced by revolving a circle about a line in its plane. The radius of the circle being revolved is referred to here as the MinorRadius and the MajorRadius is the distance from the centre of this circle to the axis of revolution. A toroidal surface is defined by the major and minor radii and the position and orientation of the surface.

C = Position.Location
x = Position.P[1]
y = Position.P[2]
z = Position.P[3] (axis of toroidal_surface)
R = MajorRadius
r = MinorRadius

σ(u,v) = C + (R + rcos v)((cosu)x + (sin u))y) + r(sinv))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) = x² + y² + z² -2R√(x²+y²) - r² + R².

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) = cosv((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.

NOTE Entity adapted from toroidal_surface defined in ISO 10303-42.

HISTORY New entity in IFC4 Addendum 2.

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
2	MajorRadius	IfcPositiveLengthMeasure		The major radius of the torus.	X
3	MinorRadius	IfcPositiveLengthMeasure		The minor radius of the torus.	X

Formal Propositions

Rule	Description
MajorLargerMinor	The attribute value of the MinorRadius shall be smaller then the value of the MajorRadius

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	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
IfcSurface
	Dim :=3	IfcDimensionCount		The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item. IFC4 CHANGE Derived attribute promoted from subtypes.	X
IfcElementarySurface
1	Position	IfcAxis2Placement3D		The position and orientation of the surface. This attribute is used in the definition of the parameterization of the surface.	X
IfcToroidalSurface
2	MajorRadius	IfcPositiveLengthMeasure		The major radius of the torus.	X
3	MinorRadius	IfcPositiveLengthMeasure		The minor radius of the torus.	X

Formal representations

XML Specification

 <xs:element name="IfcToroidalSurface" type="ifc:IfcToroidalSurface" substitutionGroup="ifc:IfcElementarySurface" nillable="true"/>

 <xs:complexType name="IfcToroidalSurface">

  <xs:complexContent>

   <xs:extension base="ifc:IfcElementarySurface">

    <xs:attribute name="MajorRadius" type="ifc:IfcPositiveLengthMeasure" use="optional"/>

    <xs:attribute name="MinorRadius" type="ifc:IfcPositiveLengthMeasure" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcToroidalSurface

 SUBTYPE OF (IfcElementarySurface);

  MajorRadius : IfcPositiveLengthMeasure;

  MinorRadius : IfcPositiveLengthMeasure;

 WHERE

  MajorLargerMinor : MinorRadius < MajorRadius;
END_ENTITY;

 EXPRESS-G diagram