IFC 4.3.x development

8.8.3.36 IfcSectionedSurface

Change log

IFC4X3_RC3

added

8.8.3.36.1 Semantic definitions at the entity

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. "sectioned surfacequot;

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. "sectioned surfacequot;

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

8.8.3.36.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignment SET [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.
IfcSectionedSurface
1 Directrix IfcCurve The curve used to define the sweeping operation
2 CrossSectionPositionsLIST [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)

8.8.3.36.2 Entity inheritance

dot_inheritance IfcSectionedSurface IfcSectionedSurface IfcSurface IfcSurface IfcSectionedSurface->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

8.8.3.36.3 Formal representations

ENTITY IfcSectionedSurface
 SUBTYPE OF (IfcSurface);
	Directrix : IfcCurve;
	CrossSectionPositions : LIST [2:?] OF IfcPointByDistanceExpression;
	CrossSections : LIST [2:?] OF IfcProfileDef;
	FixedAxisVertical : IfcBoolean;
END_ENTITY;