An IfcSectionedSpine is a representation of the shape of a three dimensional object composed by a number of planar cross sections, and a spine curve. The shape is defined between the first element of cross sections and the last element of the cross sections. A sectioned spine may be used to represent a surface or a solid but the interpolation of the shape between the cross sections is not defined.
All cross sections have to define areas by a closed profile to allow for the representation of a solid. All cross sections have to define curves by an open or closed profile to allow for the representation of a surface. The cross sections are defined by subtypes of IfcProfileDef, where the consecutive profiles may be derived by a transformation of the start profile or the previous consecutive profile.
Figure 1 illustrates an example of an IfcSectionedSpine.
Figure 2 illustrates the final result of the IfcSectionedSpine. The body (shown transparently) is not fully defined by the exchange definition.
NOTE Definition according to ISO/CD 10303-42:1992
A sectioned spine is a representation of the shape of a three dimensional object composed of a spine curve and a number of planar cross sections. The shape is defined between the first element of cross sections and the last element of this set.
NOTE A sectioned spine may be used to represent a surface or a solid but the interpolation of the shape between the cross-sections is not defined. For the representation of a solid all cross-sections are closed curves.
NOTE Entity adapted from sectioned_spine defined in ISO 10303-42.
HISTORY New entity in IFC2x.
|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.
|1||SpineCurve||IfcCompositeCurve||A single composite curve, that defines the spine curve. Each of the composite curve segments correspond to the part between two cross-sections.|
|2||CrossSections||LIST [2:?] OF IfcProfileDef||A list of at least two cross sections, each defined within the xy plane of the position coordinate system of the cross section. The position coordinate system is given by the corresponding list CrossSectionPositions.|
|3||CrossSectionPositions||LIST [2:?] OF IfcAxis2Placement3D||Position coordinate systems for the cross sections that form the sectioned spine. The profiles defining the cross sections are positioned within the xy plane of the corresponding position coordinate system.|
|Dim||INVALID||The dimensionality of the spine curve is always 3.|
ENTITY IfcSectionedSpine SUBTYPE OF (IfcGeometricRepresentationItem); SpineCurve : IfcCompositeCurve; CrossSections : LIST [2:?] OF IfcProfileDef; CrossSectionPositions : LIST [2:?] OF IfcAxis2Placement3D; DERIVE Dim : IfcDimensionCount := 3; WHERE CorrespondingSectionPositions : SIZEOF(CrossSections) = SIZEOF(CrossSectionPositions); ConsistentProfileTypes : SIZEOF(QUERY(temp <* CrossSections | CrossSections.ProfileType <> temp.ProfileType)) = 0; SpineCurveDim : SpineCurve.Dim = 3; END_ENTITY;