#### IfcSite

Natural language names

##### Semantic definitions at the entity

Entity definition

Definition from ISO 6707-1:1989: Area where construction works are undertaken.

A defined area of land, possibly covered with water, on which the project construction is to be completed. A site may be used to erect building(s) or other AEC products.

A site (IfcSite) may include a definition of the single geographic reference point for this site (global position using Longitude, Latitude and Elevation) for the project. This definition may specify an exact global position of the origin of the local placement of the IfcSite in geospatial terms or it may specify an approximate position intended for informational purposes only.

The geometrical placement of the site, defined by the IfcLocalPlacement, shall be always relative to the spatial structure element, in which this site is included, or absolute, i.e. to the world coordinate system, as established by the geometric representation context of the project. The world coordinate system, established at the IfcProject.RepresentationContexts, may include a definition of the true north within the XY plane of the world coordinate system, if provided, it can be obtained at IfcGeometricRepresentationContext.TrueNorth.

A project may span over several connected or disconnected sites. Therefore site complex provides for a collection of sites included in a project. A site can also be decomposed in parts, where each part defines a site section. This is defined by the composition type attribute of the supertype IfcSpatialStructureElements which is interpreted as follow:

- COMPLEX = site complex
- ELEMENT = site
- PARTIAL = site section

> HISTORY New entity in IFC Release 1.0.

Property Set Use Definition

The property sets relating to the IfcSite are defined by the IfcPropertySet and attached by the IfcRelDefinesByProperties relationship. It is accessible by the inverse IsDefinedBy relationship. The following property set definitions specific to the IfcSite are part of this IFC release:

- Pset_SiteCommon: common property set for all types of site

Quantity Use Definition

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

Name | Description | Value Type
NominalPerimeter | Perimeter of the Site boundary. The exact definition and calculation rules depend on the method of measurement used. | IfcQuantityLength
NominalArea | Area for this site (horizontal projections). The exact definition and calculation rules depend on the method of measurement used. | IfcQuantityArea

Spatial Structure Use Definition

The IfcSite is used to build the spatial structure of a building (that serves as the primary project breakdown and is required to be hierarchical). The spatial structure elements are linked together by using the objectified relationship IfcRelAggregates. The IfcSite references them by its inverse relationships:

- IfcSite.Decomposes -- referencing (IfcProject || IfcSite) by IfcRelAggregates.RelatingObject, If it refers to another instance of IfcSite, the referenced IfcSite needs to have a different and higher CompositionType, i.e. COMPLEX (if the other IfcSite has ELEMENT), or ELEMENT (if the other IfcSite has PARTIAL).
- IfcSite.IsDecomposedBy -- referencing (IfcSite || IfcBuilding || IfcSpace) by IfcRelAggregates.RelatedObjects. If it refers to another instance of IfcSite, the referenced IfcSite needs to have a different and lower CompositionType, i.e. ELEMENT (if the other IfcSite has COMPLEX), or PARTIAL (if the other IfcSite has ELEMENT).

If there are building elements and/or other elements directly related to the IfcSite (like a fence, or a shear wall), they are associated with the IfcSite by using the objectified relationship IfcRelContainedInSpatialStructure. The IfcIfcSite references them by its inverse relationship:

- IfcSite.ContainsElements -- referencing any subtype of IfcProduct (with the exception of other spatial structure element) by IfcRelContainedInSpatialStructure.RelatedElements.

| Figure shows the IfcSite as part of the spatial structure. In addition to the logical spatial structure, also the placement hierarchy is shown. In this example the spatial structure hierarchy and the placement hierarchy are identical. NOTE View definitions and implementation guidelines may require both hierarchies to be identical.

Geometry Use Definitions

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

Local placement

The local placement for IfcSite 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 to the IfcSpatialStructureElement of type "IfcSite", if relative placement is used (e.g. to position a site relative a a site complex, or a site section to a site).
- If the relative placement is not used, the absolute placement is defined within the world coordinate system. If there is only one site object, then this is the default situation.

Foot Print Representation

The foot print representation of IfcSite is given by either a single 2D curve (such as IfcPolyline or IfcCompositeCurve), or by a list of 2D curves (in case of inner boundaries).

The representation identifier and type of this geometric representation of IfcSite is:

- IfcShapeRepresentation.RepresentationIdentifier = 'FootPrint'
- IfcShapeRepresentation.RepresentationType = 'GeometricCurveSet'

Survey Points Representation

The survey point representation of IfcSite is defined using a set of survey points and optionally breaklines. The breaklines are restricted to only connect points given in the set of survey points. Breaklines, if given, are used to constrain the triangulation.

The representation identifier and type of this geometric representation of IfcSite is:

- IfcShapeRepresentation.RepresentationIdentifier = 'SurveyPoints'
- IfcShapeRepresentation.RepresentationType = 'GeometricSet'

| A set of survey points, given as 3D Cartesian points within the object coordinate system of the site. The set of IfcCartesianPoint is included in the set of IfcGeometricSet.Elements.
| result after facetation
| A set of survey points, given as 3D Cartesian points, and a set of break points, given as a set of lines, connecting some survey points, within the object coordinate system of the site. The set of IfcCartesianPoint and the set of IfcPolyline are included in the set of IfcGeometricSet.Elements.
| result after facetation taking the breaklines into account.

> NOTE The geometric representation of the site has been based on the ARM level description of the site_shape_representation given within the ISO 10303-225 "Building Elements using explicit shape representation".

Facetation Representation

The facetation representation of IfcSite is defined using a surface model, based on the IfcFaceBasedSurfaceModel or on the IfcShellBasedSurfaceModel. Normally the surface model is the result after triangulation of the site survey points.

The representation identifier and type of this representation of IfcSite is:

- IfcShapeRepresentation.RepresentationIdentifier = 'Facetation'
- IfcShapeRepresentation.RepresentationType = 'SurfaceModel'

Body Representation

The body (or solid model) representation of IfcSite is defined using a faceted boundary representation based on the IfcFacetedBrep or on the IfcFacetedBrepWithVoids.

The representation identifier and type of this representation of IfcSite is:

- IfcShapeRepresentation.RepresentationIdentifier = 'Body'
- IfcShapeRepresentation.RepresentationType = 'Brep'

Attribute definitions

# | Attribute | Type | Cardinality | Description | A
--- | --- | --- | --- | --- | ---
10 | RefLatitude | - |  | This attribute is out of scope for this model view definition and shall not be set. |
11 | RefLongitude | - |  | This attribute is out of scope for this model view definition and shall not be set. |
12 | RefElevation | - |  | This attribute is out of scope for this model view definition and shall not be set. |
13 | LandTitleNumber | - |  | This attribute is out of scope for this model view definition and shall not be set. |
14 | SiteAddress | - |  | This attribute is out of scope for this model view definition and shall not be set. |

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | A
--- | --- | --- | --- | --- | ---
IfcRoot
1 | GlobalId | IfcGloballyUniqueId | [1:1] | Assignment of a globally unique identifier within the entire software world. | X
2 | OwnerHistory | IfcOwnerHistory | [1:1] | Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object, NOTE: only the last modification in stored. | X
3 | Name | IfcLabel | [0:1] | Optional name for use by the participating software systems or users. For some subtypes of IfcRoot the insertion of the Name attribute may be required. This would be enforced by a where rule. | X
4 | Description | IfcText | [0:1] | Optional description, provided for exchanging informative comments. | X
IfcObjectDefinition
| IsDecomposedBy | IfcRelDecomposes @RelatingObject | S[0:?] | Reference to the decomposition relationship, that allows this object to be the composition of other objects. An object can be decomposed by several other objects. | X
| Decomposes | IfcRelDecomposes @RelatedObjects | S[0:1] | References to the decomposition relationship, that allows this object to be a part of the decomposition. An object can only be part of a single decomposition (to allow hierarchical strutures only). | X
| HasAssociations | IfcRelAssociates @RelatedObjects | S[0:?] | Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification. | X
IfcObject
5 | ObjectType | IfcLabel | [0:1] | The type denotes a particular type that indicates the object further. The use has to be established at the level of instantiable subtypes. In particular it holds the user defined type, if the enumeration of the attribute PredefinedType is set to USERDEFINED. | X
| IsDefinedBy | IfcRelDefines @RelatedObjects | S[0:?] | Set of relationships to type or property (statically or dynamically defined) information that further define the object. In case of type information, the associated IfcTypeObject contains the specific information (or type, or style), that is common to all instances of IfcObject referring to the same type. | X
IfcProduct
6 | ObjectPlacement | IfcObjectPlacement | [0:1] | Placement of the product in space, the placement can either be absolute (relative to the world coordinate system), relative (relative to the object placement of another product), or constraint (e.g. relative to grid axes). It is determined by the various subtypes of IfcObjectPlacement, which includes the axis placement information to determine the transformation for the object coordinate system. | X
7 | Representation | IfcProductRepresentation | [0:1] | Reference to the representations of the product, being either a representation (IfcProductRepresentation) or as a special case a shape representations (IfcProductDefinitionShape). The product definition shape provides for multiple geometric representations of the shape property of the object within the same object coordinate system, defined by the object placement. | X
IfcSpatialStructureElement
8 | LongName | - |  | This attribute is out of scope for this model view definition and shall not be set. |
9 | CompositionType | IfcElementCompositionEnum | [1:1] | Denotes, whether the predefined spatial structure element represents itself, or an aggregate (complex) or a part (part). The interpretation is given separately for each subtype of spatial structure element. | X
| ContainsElements | IfcRelContainedInSpatialStructure @RelatingStructure | S[0:?] | Set of spatial containment relationships, that holds those elements, which are contained within this element of the project spatial structure. NOTE The spatial containment relationship, established by IfcRelContainedInSpatialStructure, is required to be an hierarchical relationship, i.e. each element can only be assigned to 0 or 1 spatial structure element. | X
IfcSite
10 | RefLatitude | - |  | This attribute is out of scope for this model view definition and shall not be set. |
11 | RefLongitude | - |  | This attribute is out of scope for this model view definition and shall not be set. |
12 | RefElevation | - |  | This attribute is out of scope for this model view definition and shall not be set. |
13 | LandTitleNumber | - |  | This attribute is out of scope for this model view definition and shall not be set. |
14 | SiteAddress | - |  | This attribute is out of scope for this model view definition and shall not be set. |

##### Definitions applying to AISC Model View

Instance diagram

Concept usage

Spatial Composition

The Spatial Composition concept applies to this entity as shown in Table 7.

RelatingObject
IfcProject
Table 7 — IfcSite Spatial Composition

Exchange |
--- | ---
Import | R
Export | R

Spatial Decomposition

The Spatial Decomposition concept applies to this entity as shown in Table 8.

RelatedOjbects
IfcBuilding
Table 8 — IfcSite Spatial Decomposition

Exchange |
--- | ---
Import | R
Export | R

Placement

The Placement concept applies to this entity.

Exchange |
--- | ---
Import | R
Export | R

Concept inheritance

# | Concept | Model View
--- | --- | ---
IfcSite
| Spatial Composition | AISC Model View
| Spatial Decomposition | AISC Model View
| Placement | AISC Model View

##### Formal representations

XSD Specification
`<xs:element name="IfcSite" type="ifc:IfcSite" substitutionGroup="ifc:IfcSpatialStructureElement" nillable="true"/>
<xs:complexType name="IfcSite">
<xs:complexContent>
<xs:extension base="ifc:IfcSpatialStructureElement"/>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`ENTITY IfcSite
SUBTYPE OF (IfcSpatialStructureElement);
RefLatitude : OPTIONAL IfcStrippedOptional;
RefLongitude : OPTIONAL IfcStrippedOptional;
RefElevation : OPTIONAL IfcStrippedOptional;
LandTitleNumber : OPTIONAL IfcStrippedOptional;
SiteAddress : OPTIONAL IfcStrippedOptional;
END_ENTITY;

EXPRESS-G diagram

`

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