IfcPolygonalBoundedHalfSpace

Semantic definitions at the entity

Entity definition

The polygonal bounded half space is a special subtype of a half space solid, where the material of the half space used in Boolean expressions is bounded by a polygonal boundary. The base surface of the half space is positioned by its normal relative to the object coordinate system (as defined at the supertype IfcHalfSpaceSolid), and its polygonal (with or without arc segments) boundary is defined in the XY plane of the position coordinate system established by the Position attribute, the subtraction body is extruded perpendicular to the XY plane of the position coordinate system, that is, into the direction of the positive Z axis defined by the Position attribute.

The boundary is defined by a 2 dimensional polyline (or 2 dimensional composite curve, consisting of straight segments and circular arc segments) within the XY plane of the position coordinate system. The side of the surface which is in the half space is determined by the surface normal and the agreement flag. If the agreement flag is TRUE, then the subset is the one the normal points away from. If the agreement flag is FALSE, then the subset is the one the normal points into.

NOTE A polygonal bounded half space is not a subtype of IfcSolidModel, half space solids are only useful as operands in Boolean expressions.

Figure 316 illustrates a polygonal bounded half space.

Black coordinates indicate the object coordinate system (usually provided by IfcLocalPlacement).
Green coordinates indicate the position coordinate system; the PolygonalBoundary is given within this coordinate system. It is provided by IfcPolygonalBoundedHalfSpace.Position. This coordinate system is relative to the object coordinate system. The extrusion direction of the subtraction body is the positive Z axis.
Red coordinates indicate the normal of the plane. It is provided by the BaseSurface (IfcSurface.Position). This normal is also relative to the object coordinate system.

Figure 316 — Polygonal half space geometry

The polygonal bounded half space is used to limit the volume of the half space in Boolean difference expressions. Only the part that is defined by a theoretical intersection between the half space solid and an extruded area solid, defined by extruding the polygonal boundary, is used for Boolean expressions.

The PolygonalBoundary defines the 2D polyline which bounds the effectiveness of the half space in Boolean expressions. The BaseSurface is defined by a plane, and the normal of the plane together with the AgreementFlag defines the side of the material of the half space.

HISTORY New entity in IFC2x.

Informal Propositions:

The IfcPolyline or the IfcCompositeCurve providing the PolygonalBoundary shall be closed.
If the PolygonalBoundary is given by an IfcCompositeCurve, it shall only have IfcCompositeCurveSegment's of type IfcPolyline, or IfcTrimmedCurve (having a BasisCurve of type IfcLine, or IfcCircle)
The BaseSurface defined at supertype IfcHalfSpaceSolid shall be of type IfcPlane
The normal of the plane, being the BaseSurface, shall not be perpendicular to the z-axis of the position coordinate system

Attribute definitions

#	Attribute	Type	Cardinality	Description	C
3	Position	IfcAxis2Placement3D	[1:1]	Definition of the position coordinate system for the bounding polyline ~~and the base surface~~.	X
4	PolygonalBoundary	IfcBoundedCurve	[1:1]	Two-dimensional ~~polyline~~ bounded curve, defined in the xy plane of the position coordinate system.	X

Formal Propositions

Rule	Description
BoundaryDim	The bounding polyline should have the dimensionality of 2.
BoundaryType	Only bounded curves of type IfcCompositeCurve, or IfcPolyline are valid boundaries.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	C
IfcRepresentationItem
	LayerAssignment	IfcPresentationLayerAssignment @AssignedItems	S[0:1]	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.	X
	StyledByItem	IfcStyledItem @Item	S[0:1]	Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.	X
IfcGeometricRepresentationItem
IfcHalfSpaceSolid
1	BaseSurface	IfcSurface	[1:1]	Surface defining side of half space.	X
2	AgreementFlag	IfcBoolean	[1:1]	The agreement flag is TRUE if the normal to the BaseSurface points away from the material of the IfcHalfSpaceSolid. Otherwise it is FALSE.	X
	Dim :=3	IfcDimensionCount	[1:1]	The space dimensionality of this class, it is always 3	X
IfcPolygonalBoundedHalfSpace
3	Position	IfcAxis2Placement3D	[1:1]	Definition of the position coordinate system for the bounding polyline ~~and the base surface~~.	X
4	PolygonalBoundary	IfcBoundedCurve	[1:1]	Two-dimensional ~~polyline~~ bounded curve, defined in the xy plane of the position coordinate system.	X

Formal representations

XSD Specification

 <xs:element name="IfcPolygonalBoundedHalfSpace" type="ifc:IfcPolygonalBoundedHalfSpace" substitutionGroup="ifc:IfcHalfSpaceSolid" nillable="true"/>

 <xs:complexType name="IfcPolygonalBoundedHalfSpace">

  <xs:complexContent>

   <xs:extension base="ifc:IfcHalfSpaceSolid">

    <xs:sequence>

     <xs:element name="Position" type="ifc:IfcAxis2Placement3D" nillable="true"/>

     <xs:element name="PolygonalBoundary" type="ifc:IfcBoundedCurve" nillable="true"/>

    </xs:sequence>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcPolygonalBoundedHalfSpace

 SUBTYPE OF (IfcHalfSpaceSolid);

  Position : IfcAxis2Placement3D;

  PolygonalBoundary : IfcBoundedCurve;

 WHERE

  BoundaryDim : PolygonalBoundary.Dim = 2;
  BoundaryType : SIZEOF(TYPEOF(PolygonalBoundary) * [
  'IFCGEOMETRYRESOURCE.IFCPOLYLINE', 
  'IFCGEOMETRYRESOURCE.IFCCOMPOSITECURVE']
) = 1;
END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
IFC4 Addendum 1
IfcPolygonalBoundedHalfSpace
AgreementFlag	MODIFIED	Type changed from BOOLEAN to IfcBoolean.

	Halbraum - eingeschränkter Gültigkeitsbereich
	Polygonal Bounded Half Space