There are two different types of opening elements:

• an opening, where the thickness of the opening is greater or equal to the thickness of the element;
• a recess or niche, where the thickness of the recess is smaller than the thickness of the element.

The inherited attribute ObjectType should be used to capture the differences, the attribute is set to 'Opening' for an opening or to 'Recess' for a recess or niche. If the value for ObjectType is omitted, opening is assumed.

An IfcOpeningElement has to be inserted into a building element (all subtypes of IfcBuildingElement) by using the IfcRelVoidsElement relationship. It is also directly liked to the spatial structure of the project (and here normally to the IfcBuildingStorey) by using the IfcRelContainsInSpatialStructure relationship.

The quantities relating to the space are defined by the IfcElementQuantity and attached by the IfcRelDefinesByProperties. The following quantities are foreseen, but will be subjected to the local standard of measurement:

HISTORY New entity in IFC Release 1.0
ISSUE See issue log for changes made in IFC Release 1.5.1. See issue and change log for changes made in IFC Release 2.x

Geometry Use Definitions:

The geometric representation of IfcOpeningElement is given by the IfcProductDefinitionShape and IfcLocalPlacement allowing multiple geometric representations.

Local Placement

The local placement for IfcOpeningElement is defined in its supertype IfcProduct. It is defined by the IfcLocalPlacement, which defines the local coordinate system that is referenced by all geometric representations.

• The PlacementRelTo relationship of IfcLocalPlacement should point to the local placement of the same element, which is voided by the opening, i.e. refered to by VoidsElement.RelatingBuildingElement.

Standard Geometric Representation using Swept Solid Representation

The standard geometric representation of IfcOpeningElement is defined using the swept area solid geometry. The attribute RepresentationType of IfcShapeRepresentation should have the value 'SweptSolid'. The following additional constraints apply to the swept solid representation:

• Solid: IfcExtrudedAreaSolid is required.
• Profile: IfcRectangleProfileDef shall be supported.
• Extrusion: The profile shall be extruded horizontally (i.e. perpendicular to the extrusion direction of the voided element), e.g. for wall openings, or vertically (i.e. in the extrusion direction of the voided element), e.g., for floor openings.

Special agreement for defining openings in round building elements, e.g., in round walls. The opening width, in case of a rectangular opening equal with the IfcRectangleProfileDef.XDim, is defined as the straight line distance between two parallel jambs. If the jambs are defined radial (to the center of the arc used to define the round wall) then the opening width is defined to be the outer arc length.

NOTE: In case of non-parallel jambs, the geometry expression is not an extruded area solid, it has to be represented using other types of representations.

EXAMPLE

The following interpretation of dimension parameter applies for rectangular openings: IfcRectangleProfileDef.YDim interpreted as opening width IfcRectangleProfileDef.XDim interpreted as opening height NOTE: Rectangles are now defined centric, the placement location has to be set: IfcCartesianPoint(XDim/2,YDim/2)

Advanced Geometric Representation using Swept Solid Representation

The advanced geometric representation of IfcOpeningElement is defined using the swept area solid geometry. The following additional constraints apply to the swept solid representation:

• Solid: see standard geometric representation,
• Profile: IfcRectangleProfileDef, IfcCircleProfileDef and IfcArbitraryClosedProfileDef shall be supported.
• Extrusion: see standard geometric representation