IFC 4.3.x development

8.9.3.66 IfcSphericalSurface

Change log

IFC4

added

8.9.3.66.1 Semantic definitions at the entity

The IfcSphericalSurface is a bounded elementary surface. 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 spherical surface.
  • SELF\IfcElementarySurface.Position.Position[3]: The z axis points at its positve direction towards the north pole, and by its negative directions towards the south pole.

NOTE  Definition according to ISO/CD 10303-42:1992
An IfcSphericalSurface is a type of an elementary surface, which is at a constant distance (the radius) from a central point. A spherical surface is defined by the radius and the location and orientation of the surface.

The data is to be interpreted as follows:

C = Position.Location
x = Position.P[1]
y = Position.P[2]
z = Position.P[3] (axis of spherical surface)
R = Radius and the surface is parametrised as

σ(u,v) = C + R cos v ((cos u) x + (sin u) y) + R(sin v) z where the parametrisation range is 0 ≤ u ≤ 360 degrees and -90 ≤ v ≤ 90 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^ - 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,

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

HISTORY  New entity in IFC4 Addendum 2.

8.9.3.66.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignmentSET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment 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.
IfcGeometricRepresentationItem
IfcSurface
Dim INVALID The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.

> IFC4 CHANGE Derived attribute promoted from subtypes.
IfcElementarySurface
1 Position IfcAxis2Placement3D The position and orientation of the surface. This attribute is used in the definition of the parameterization of the surface.
IfcSphericalSurface
2 Radius IfcPositiveLengthMeasure The radius of the sphere.

8.9.3.66.2 Entity inheritance

dot_inheritance IfcSphericalSurface IfcSphericalSurface IfcElementarySurface IfcElementarySurface IfcSphericalSurface->IfcElementarySurface IfcElementarySurface_children 3 more... IfcElementarySurface_children->IfcElementarySurface IfcSurface IfcSurface IfcElementarySurface->IfcSurface IfcSurface_children 3 more... IfcSurface_children->IfcSurface IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcSurface->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.9.3.66.3 Formal representations

ENTITY IfcSphericalSurface
 SUBTYPE OF (IfcElementarySurface);
	Radius : IfcPositiveLengthMeasure;
END_ENTITY;