Definition from IAI: The IfcOpeningElement stands for opening, recess or chase, all reflecting voids. It represents a void within any element that has physical manifestation. Openings must be handled by all sectors and disciplines in AEC/FM industry, therefore the interoperability for opening elements is provided at this high level.
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
- the attribute is set 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:
| Name | Description | Value Type |
| OpeningArea | Area of the opening as viewed by an elevation view (for wall openings) or as viewed by a ground floor view (for floor openings). The exact definition and calculation rules depend on the method of measurement used. | IfcAreaQuantity |
HISTORY New entity in IFC Release 1.0
IFC2x PLATFORM CHANGE: The intermediate ABSTRACT supertypes IfcFeatureElement and IfcFeatureSubtraction have been added between IfcElement and IfcOpeningElement with upward compatibility.
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.
Geometric Representation
Currently, the use of 'SweptSolid', 'Brep', and 'MappedRepresentation' representation is supported.
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, IfcCircleProfileDef and IfcArbitraryClosedProfileDef 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 for openings
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The following interpretation of dimension parameter applies for rectangular openings:
NOTE: Rectangles are now defined centric, the placement location has to be set:
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EXAMPLE for recesses
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The following interpretation of dimension parameter applies for rectangular recess:
NOTE: Rectangles are now defined centric, the placement location has to be set:
NOTE: The local placement directions for the IfcOpeningRecess are only given as an example, other directions are valid as well. |
Brep Representation
The general b-rep geometric representation of IfcOpeningRecess is defined using the Brep geometry. The Brep representation allows for the representation of complex element shape. It is ensured by assigning the value 'Brep' to the RepresentationType attribute of IfcShapeRepresentation The RepresentationIdentifier of IfcShapeRepresentation should then have the value 'Body'.
MappedRepresentation
The new mapped item, IfcMappedItem, should be used if appropriate as it allows for reusing the geometry definition of the IfcOpeningElementType or IfcOpeningRecessType at occurrences of the same type. In this case the IfcShapeRepresentation.RepresentationType should have the value 'MappedRepresentation'.