IfcRoof

IfcRoof

Definition from IAI: The roof entity (IfcRoof) is a description of the total roof. It acts as a container entity, that aggregates all components of the roof, it represents. The aggregation is handled via the IfcRelAggregates relationship, relating a roof (IfcRoof) with the related roof entities, like slabs (IfcSlab), rafters and purlins (IfcBeam), or other (included) roofs, such as dormers (IfcRoof).

The quantities relating to the roof 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
TotalRoofArea	Total (exposed) area of all roof slabs belonging to the roof. The exact definition and calculation rules depend on the method of measurement used.	IfcAreaQuantity

HISTORY: New Entity in IFC Release 2.0
ISSUES: See issue and change log for changes made in IFC Release 2.x

Geometry Use Definitions:

The geometric representation of IfcRoof is given by the IfcProductDefinitionShape, allowing multiple geometric representation. Independent geometric representations should only be used when the IfcRoof is not defined as an aggregate. If defined as an aggregate, the geometric representation is the sum of the representation of the components within the aggregate.

Local Position

The local placement for IfcRoof 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 shall point (if given) to the local placement of the same IfcSpatialStructureElement , which is used in the ContainedInStructure inverse attribute, or to a spatial structure element at a higher level, referenced by that.
If the relative placement is not used, the absolute placement is defined within the world coordinate system.

If the LocalPlacement is given for the IfcRoof, then all components, which are aggregated to the roof should use this placement as their relative placement.

Geometric Representation

If the IfcRoof has components (referenced by SELF\IfcObject.IsDecomposedBy) then no independent geometric representation shall defined for the IfcRoof. The IfcRoof is then geometrically represented by the geometric representation of its components. The components are accessed via SELF\IfcObject.IsDecomposedBy[1].RelatedObjects.

If the IfcRoof has no components defined (empty set of SELF\IfcObject.IsDecomposedBy) then the IfcRoof may be represented by an IfcShapeRepresentation with the RepresentationType = 'Brep'.

Illustration:

IfcRoof defining only the local placement for all components.

EXPRESS specification:

ENTITY IfcRoof

SUBTYPE OF (

IfcBuildingElement);

ShapeType

IfcRoofTypeEnum;

WHERE

WR1

(HIINDEX(SELF\IfcObject.IsDecomposedBy) = 0) OR ((HIINDEX(SELF\IfcObject.IsDecomposedBy) = 1) AND (NOT(EXISTS(SELF\IfcProduct.Representation))));

END_ENTITY;

Attribute definitions:

ShapeType

Predefined shape types for a roof that are specified in an enumeration.

Formal Propositions:

WR1

Either the roof is not decomposed into its roof slabs (the roof can have independent geometry), or the geometry shall not be given at IfcRoof directly.

References (1):

Name

Type

Referred through

Express-G

IfcBuildingElement

Entity

Subtype

Diagram 1

Inheritance graph

ENTITY IfcRoof;

ENTITY IfcRoot;

GlobalId

IfcGloballyUniqueId;

OwnerHistory

IfcOwnerHistory;

Name

OPTIONAL IfcLabel;

Description

OPTIONAL IfcText;

ENTITY IfcObject;

ObjectType

OPTIONAL IfcLabel;

INVERSE

IsDefinedBy

SET OF IfcRelDefines FOR RelatedObjects;

HasAssociations

SET OF IfcRelAssociates FOR RelatedObjects;

HasAssignments

SET OF IfcRelAssigns FOR RelatedObjects;

Decomposes

SET OF IfcRelDecomposes FOR RelatedObjects;

IsDecomposedBy

SET [0:1] OF IfcRelDecomposes FOR RelatingObject;

ENTITY IfcProduct;

ObjectPlacement

OPTIONAL IfcObjectPlacement;

Representation

OPTIONAL IfcProductRepresentation;

INVERSE

ReferencedBy

SET OF IfcRelAssignsToProduct FOR RelatingProduct;

ENTITY IfcElement;

Tag

OPTIONAL IfcIdentifier;

INVERSE

ConnectedTo

SET OF IfcRelConnectsElements FOR RelatingElement;

ConnectedFrom

SET OF IfcRelConnectsElements FOR RelatedElement;

ContainedInStructure

SET [0:1] OF IfcRelContainedInSpatialStructure FOR RelatedElements;

ENTITY IfcBuildingElement;

INVERSE

ProvidesBoundaries

SET OF IfcRelSpaceBoundary FOR RelatedBuildingElement;

HasOpenings

SET OF IfcRelVoidsElement FOR RelatingBuildingElement;

FillsVoids

SET [0:1] OF IfcRelFillsElement FOR RelatedBuildingElement;

ENTITY IfcRoof;

ShapeType

IfcRoofTypeEnum;

END_ENTITY;