A kind of surface constructed by sweeping potentially varying open cross sections along a curve horizontally (or near horizontally). The surface is generated by sweeping the CrossSections between CrossSectionPositions; linear interpolation is assumed, unless transitions curves between cross section points are indicated by OpenCrossProfileDef.Tags. The CrossSections are oriented with the Y axis of each profile facing upwards in +Z direction or vertically perpendicular to the Directrix, depending on the Attribute FixedAxisVertical value.
In case of branching longitudinal breaklines, the SectionedSurface may use OpenCrossProfileDef instances with varying number of cross section points. In that case, the point in two consecutive cross sections that are connected are identified by the same tag value.
Formal propositions: * The curve entity which is the underlying directrix shall have the dimensionality of 3. * The profile type shall be CURVE within the list of the profiles defining the cross sections. * The entity type for each section must be the same. * The list of cross sections and the list of cross section positions shall be of the same size.
Informal Propositions: No two consecutive sections shall intersect. * If the directrix is not tangent continuous, the resulting surface is created by a miter at half angle between the two segments. * Very sharp edges may result in nearly impossible miter; implementer agreements may define acceptable limits for tangent discontinuity or require the directrix to be tangent continuous. * The directrix shall not intersect
|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||Directrix||IfcCurve||The curve used to define the sweeping operation|
|2||CrossSectionPositions||LIST [2:?] OF IfcPointByDistanceExpression||List of distance expressions in sequentially increasing order paired with CrossSections, indicating the position of the corresponding section along the Directrix.|
|3||CrossSections||LIST [2:?] OF IfcProfileDef||List of cross sections in sequential order along the Directrix|
|4||FixedAxisVertical||IfcBoolean||Indicates whether Sections are oriented with the Y axis of each profile facing upwards in +Z direction (True), or vertically perpendicular to the Directrix varying according to slope (False)|
ENTITY IfcSectionedSurface SUBTYPE OF (IfcSurface); Directrix : IfcCurve; CrossSectionPositions : LIST [2:?] OF IfcPointByDistanceExpression; CrossSections : LIST [2:?] OF IfcProfileDef; FixedAxisVertical : IfcBoolean; END_ENTITY;