The cylindrical surface is a surface unbounded in the direction of z. Bounded cylindrical surfaces are defined by using a subtype of IfcBoundedSurface with BasisSurface being a cylindrical surface.
NOTE 1 A bounded cylindrical surface can be defined by an IfcRectangularTrimmedSurface with BasisSurface being the cylindrical surface and U1 = 0°, U2 = 360° and V1 = lower bound in z, V2 = upper bound in z (if the plane angle measure is degree). A bounded cylindrical arc surface is provided with |U1 - U2| < 360° (assuming the Usense and Vsense agree to the sense of the basis surface).
NOTE 2 A non-rectangular bounded cylindrical surface, e.g. the surface of a round wall underneath a sloped roof, cab be defined by an IfcCurveBoundedSurface with IfcBoundaryCurve's, being a collection of p-curve segments. A p-curve is curve which lies on the basis of a surface and is defined in the parameter space of that surface.
The inherited attributes are interpreted as
NOTE Definition according to ISO/CD 10303-42:1992
A cylindrical surface is a surface at a constant distance (the radius) from a straight line. A cylindrical surface is defined by its radius and its orientation and location. The data is to be interpreted as follows:C = Position.Location x = Position.P y = Position.P z = Position.P R = Radiusand the surface is parameterized as:
where the parametric range is -∞ < u,v < ∞ .
In the above parameterization the length unit for the unit vectors z is equal to that of the radius R. In the placement coordinate system defined above, the surface is represented by the equation S = 0, where
The positive direction of the normal to the surface at any point on the surface is given by
, or as unit normal by
The direction of the normal is away from the axis of the cylinder.
NOTE Entity adapted from cylindrical_surface defined in ISO 10303-42.
HISTORY New entity in IFC4.
|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.|
> 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.
|Dim||INVALID||The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.|
> IFC4 CHANGE Derived attribute promoted from subtypes.
|1||Position||IfcAxis2Placement3D||The position and orientation of the surface. This attribute is used in the definition of the parameterization of the surface.|
|2||Radius||IfcPositiveLengthMeasure||The radius of the cylindrical surface.|
ENTITY IfcCylindricalSurface SUBTYPE OF (IfcElementarySurface); Radius : IfcPositiveLengthMeasure; END_ENTITY;