IFC 4.3.x development

8.8.3.35 IfcSectionedSpine

Change log

IFC4

additionswhere_rulesConsistentProfileTypes
additionswhere_rulesCorrespondingSectionPositions
additionswhere_rulesSpineCurveDim
deletionswhere_rulesWR1
deletionswhere_rulesWR2
deletionswhere_rulesWR3

8.8.3.35.1 Semantic definitions at the entity

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.

The spine curve shall be of type IfcCompositeCurve, each of its segments represented by IfcCompositeCurveSegment shall correspond to the part between exactly two consecutive cross-sections.

Figure 1 illustrates an example of an IfcSectionedSpine.

  • The SpineCurve is given by an IfcCompositeCurve with two Segments. The Segments[1] has a ParentCurve of type IfcPolyline and a Transition = CONTSAMEGRADIENT. The Segments[2] has a ParentCurve of type IfcTrimmedCurve and a Transition = DISCONTINUOUS.
  • Each CrossSectionPosition lies at a start or end point of the Segments.
  • Each CrossSections are inserted by the CrossSectionPositions. The first two cross sections are of type IfcRectangleProfileDef, the third is of type IfcDerivedProfileDef.

"spine 1"

Figure 2 illustrates the final result of the IfcSectionedSpine. The body (shown transparently) is not fully defined by the exchange definition.

"render"

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.

Informal Propositions:

  1. none of the cross sections, after being placed by the cross section positions, shall intersect
  2. none of the cross sections, after being placed by the cross section positions, shall lie in the same plane
  3. the local origin of each cross section position shall lie at the beginning or end of a composite curve segment.

8.8.3.35.1 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
IfcSectionedSpine
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 CrossSectionPositionsLIST [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.

8.8.3.35.2 Entity inheritance

dot_inheritance IfcSectionedSpine IfcSectionedSpine IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcSectionedSpine->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.8.3.35.3 Formal representations

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[1].ProfileType <> temp.ProfileType)) = 0;
	SpineCurveDim : SpineCurve.Dim = 3;
END_ENTITY;