5.4.2.20 IfcGeographicElement

An IfcGeographicElement is a generalization of all elements within a geographical landscape. It includes occurrences of typical geographical element, often referred to as features, such as roads, zones, trees, etc. Common type information behind several occurrences of IfcGeographicElement is provided by the IfcGeographicElementType.

HISTORY New entity in Release IFC2x4.

Type Use Definition

An IfcGeographicElement defines the occuurence of any element within a geographic landscape, common information about geographic elements is handled by IfcGeographicElementType. The IfcGeographicElementType (if present) may establish the common type name, usage (or predefined) type, common set of properties and common shape representations (using IfcRepresentationMap). The IfcGeographicElementType is attached using the IfcRelDefinedByType.RelatingType objectified relationship and is accessible by the inverse IsDefinedBy attribute.

Classification Use Definition

An IfcGeographicElement might be further qualified by referencing a feature catalog as a particular classification. The feature classification is assigned using the inverse relationship HasAssociations pointing to IfcClassificationReference. The attributes should have the following meaning:

• Catalog : IfcClassification.Name
• Identity: IfcClassificationReference.ItemReference
• ElementName: IfcClassificationReference.Name
• if there is a differentiation between an main element and a sub element without a unique notation facet, then the main element and sub element(s) can be established by using the subtype
  • IfcClassificationReferenceWithFacets.ItemReferenceFacets

Containment Use Definition

The IfcGeographicElement, as any subtype of IfcElement, may participate in two different containment relationships. The first (and in most implementation scenarios mandatory) relationship is the hierachical spatial containment, the second (optional) relationship is the aggregation within an element assembly.

• The IfcGeographicElement is places within the project spatial hierarchy using the objectified relationship IfcRelContainedInSpatialStructure, refering to it by its inverse attribute SELF\IfcElement.ContainedInStructure. Subtypes of IfcSpatialStructureElement are valid spatial containers, with IfcSite being the default container.
• The IfcGeographicElement may be aggregated into an element assembly using the objectified relationship IfcRelAggregates, refering to it by its inverse attribute SELF\IfcObjectDefinition.Decomposes. Any subtype of IfcElement can be an element assembly, with IfcElementAssembly as a special focus subtype. In this case it should not be additionally contained in the project spatial hierarchy, i.e. SELF\IfcElement.ContainedInStructure should be NIL.

Geometry Use Definitions

The geometric representation of IfcGeographicElement is given by the IfcProductDefinitionShape, allowing multiple geometric representation.

Local Placement

The local placement for IfcGeographicElement 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.

Geometric Representation

GeometricCurveSet and GeometricSet Representation

The standard representation of IfcGeographicElement is defined using 'GeometricCurveSet' or, when including surfaces, the 'GeometricSet' geometry. This also supports a 2D representation of IfcGeographicElement.

The following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used:

• RepresentationIdentifier : 'FootPrint' for 2D representation
• RepresentationType : 'GeometricCurveSet' or 'GeometricSet'

Annotation2D Representation

Additional annotation objects, like text or hatching, and style information to the 2D representations, may be exchanged using the 'Annotation2D' representation. Style information is assigned to the geometric representation items within the set of Items at IfcShapeRepresentation using the inverse StyledByItem relationship.

The following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used:

• RepresentationIdentifier : 'FootPrint' for 2D representation
• RepresentationType : 'Annotation2D'

SurfaceModel and Brep Representation

For full 3D representations, the use of 'SurfaceModel' and 'Brep' geometry is supported. This supports a 3D representation, including support for 3D digital terrain models.

The following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used:

• RepresentationIdentifier : 'Body' for 3D representation
• RepresentationType : 'SurfaceModel' or 'Brep'

When using the IfcGeographicElement in conjunction with the IfcGeographicElementType having RepresentationMaps defined, the geometric representation of IfcGeographicElement shall be based on 'MappedRepresentation', referencing the IfcRepresentationMap given at the type object.

The following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used:

• RepresentationIdentifier : 'FootPrint' for 2D representation, 'Body' for 3D representation
• RepresentationType : 'MappedRepresentation'

EXPRESS Specification

EXPRESS-G Specification

Attribute Definitions

Formal Propositions

Inheritance Graph