IfcGrid

Semantic definitions at the entity

Entity definition

IfcGrid ia a planar design grid defined in 3D space used as an aid in locating structural and design elements. The position of the grid (ObjectPlacement) is defined by a 3D coordinate system (and thereby the design grid can be used in plan, section or in any position relative to the world coordinate system). The position can be relative to the object placement of other products or grids. The XY plane of the 3D coordinate system is used to place the grid axes, which are 2D curves (for example, line, circle, arc, polyline).

The inherited attributes Name and Description can be used to define a descriptive name of the grid and to indicate the grid's purpose. A grid is defined by (normally) two, or (in case of a triangular grid) three lists of grid axes. The following figures shows some examples.

A grid may support a rectangular layout as shown in Figure 158, a radial layout as shown in Figure 159, or a triangular layout as shown in Figure 160.

NOTE The PredefinedType denotes the type of grid that is represented by IfcGrid. The instantiation of IfcGridAxis's has to agree to the PredefinedType, if provided.

NOTE The grid axes, defined within the design grid, are those elements to which project objects will be placed relatively using the IfcGridPlacement.


Figure 158 — Grid rectangular layout	Figure 159 — Grid radial layout	Figure 160 — Grid triangular layout

HISTORY New entity in IFC1.0.

IFC4 CHANGE The attribute PredefinedType has been added at the end of the attribute list.

Informal Propositions:

Grid axes, which are referenced in different lists of axes (UAxes, VAxes, WAxes) shall not be parallel.
Grid axes should be defined such as there are no two grid axes which intersect twice (see Figure 189).

NOTE Left side: ambiguous intersections A1 and A2, a grid containing such grid axes is not a valid design grid; Right side: the conflict can be resolved by splitting one grid axis in a way, such as no ambiguous intersections exist.

Figure 161 — Grid intersections

Attribute definitions

#	Attribute	Type	Cardinality	Description	G
8	UAxes	IfcGridAxis	L[1:?]	List of grid axes defining the first row of grid lines.	X
9	VAxes	IfcGridAxis	L[1:?]	List of grid axes defining the second row of grid lines.	X
10	WAxes	IfcGridAxis	? L[1:?]	List of grid axes defining the third row of grid lines. It may be given in the case of a triangular grid.	X
11	PredefinedType	IfcGridTypeEnum	?	Predefined types to define the particular type of the grid. IFC4 Change New attribute.	X

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	G
IfcRoot
1	GlobalId	IfcGloballyUniqueId		Assignment of a globally unique identifier within the entire software world.	X
2	OwnerHistory	IfcOwnerHistory	?	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 - either as addition, deletion or modification. IFC4 CHANGE The attribute has been changed to be OPTIONAL.	X
3	Name	IfcLabel	?	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	?	Optional description, provided for exchanging informative comments.	X
IfcObjectDefinition
	HasAssignments	IfcRelAssigns @RelatedObjects	S[0:?]	Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.	X
	Nests	IfcRelNests @RelatedObjects	S[0:1]	References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been added and separated from Decomposes defined at IfcObjectDefinition.	X
	IsNestedBy	IfcRelNests @RelatingObject	S[0:?]	References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types). IFC4 CHANGE The inverse attribute datatype has been added and separated from IsDecomposedBy defined at IfcObjectDefinition.	X
	HasContext	IfcRelDeclares @RelatedDefinitions	S[0:1]	References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object. IFC4 CHANGE The inverse attribute datatype has been added.	X
	IsDecomposedBy	IfcRelAggregates @RelatingObject	S[0:?]	References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	X
	Decomposes	IfcRelAggregates @RelatedObjects	S[0:1]	References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only). IFC4 CHANGE The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.	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	?	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
	IsDeclaredBy	IfcRelDefinesByObject @RelatedObjects	S[0:1]	Link to the relationship object pointing to the declaring object that provides the object definitions for this object occurrence. The declaring object has to be part of an object type decomposition. The associated IfcObject, or its subtypes, contains the specific information (as part of a type, or style, definition), that is common to all reflected instances of the declaring IfcObject, or its subtypes. IFC4 CHANGE New inverse relationship, change made with upward compatibility for file based exchange.	X
	Declares	IfcRelDefinesByObject @RelatingObject	S[0:?]	Link to the relationship object pointing to the reflected object(s) that receives the object definitions. The reflected object has to be part of an object occurrence decomposition. The associated IfcObject, or its subtypes, provides the specific information (as part of a type, or style, definition), that is common to all reflected instances of the declaring IfcObject, or its subtypes. IFC4 CHANGE New inverse relationship, change made with upward compatibility for file based exchange.	X
	IsTypedBy	IfcRelDefinesByType @RelatedObjects	S[0:1]	Set of relationships to the object type that provides the type definitions for this object occurrence. The then associated IfcTypeObject, or its subtypes, contains the specific information (or type, or style), that is common to all instances of IfcObject, or its subtypes, referring to the same type. IFC4 CHANGE New inverse relationship, the link to IfcRelDefinesByType had previously be included in the inverse relationship IfcRelDefines. Change made with upward compatibility for file based exchange.	X
	IsDefinedBy	IfcRelDefinesByProperties @RelatedObjects	S[0:?]	Set of relationships to property set definitions attached to this object. Those statically or dynamically defined properties contain alphanumeric information content that further defines the object. IFC4 CHANGE The data type has been changed from IfcRelDefines to IfcRelDefinesByProperties with upward compatibility for file based exchange.	X
IfcProduct
6	ObjectPlacement	IfcObjectPlacement	?	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	?	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
	ReferencedBy	IfcRelAssignsToProduct @RelatingProduct	S[0:?]	Reference to the IfcRelAssignsToProduct relationship, by which other products, processes, controls, resources or actors (as subtypes of IfcObjectDefinition) can be related to this product.	X
IfcPositioningElement
	ContainedInStructure	IfcRelContainedInSpatialStructure @RelatedElements	S[0:1]	Relationship to a spatial structure element, to which the positioning element is primarily associated. IFC2x CHANGE The inverse relationship has been added to IfcGrid with upward compatibility IFC4 CHANGE The inverse relationship has been promoted from IfcGrid to this new supertype with upward compatibility	X
IfcGrid
8	UAxes	IfcGridAxis	L[1:?]	List of grid axes defining the first row of grid lines.	X
9	VAxes	IfcGridAxis	L[1:?]	List of grid axes defining the second row of grid lines.	X
10	WAxes	IfcGridAxis	? L[1:?]	List of grid axes defining the third row of grid lines. It may be given in the case of a triangular grid.	X
11	PredefinedType	IfcGridTypeEnum	?	Predefined types to define the particular type of the grid. IFC4 Change New attribute.	X

#	Concept	Template	Model View
IfcRoot
	Identity	Software Identity	General Usage
	Revision Control	Revision Control	General Usage
IfcObjectDefinition
	Classification Association	Classification Association	General Usage
IfcObject
	Object User Identity	Object User Identity	General Usage
	Object Predefined Type	Object Predefined Type	General Usage
	Object Typing	Object Typing	General Usage
	Property Sets for Objects	Property Sets for Objects	General Usage
	Property Sets with Override	Property Sets with Override	General Usage
IfcProduct
	Product Placement	Product Placement	General Usage
	Product Geometric Representation	Product Geometric Representation	General Usage
IfcPositioningElement
	Placement	Product Local Placement	General Usage
	Footprint Geometry	FootPrint Geometry	General Usage

Formal representations

XML Specification

 <xs:element name="IfcGrid" type="ifc:IfcGrid" substitutionGroup="ifc:IfcPositioningElement" nillable="true"/>

 <xs:complexType name="IfcGrid">

  <xs:complexContent>

   <xs:extension base="ifc:IfcPositioningElement">

    <xs:sequence>

     <xs:element name="UAxes">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcGridAxis" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcGridAxis"/>

       <xs:attribute ref="ifc:cType" fixed="list-unique"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

     <xs:element name="VAxes">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcGridAxis" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcGridAxis"/>

       <xs:attribute ref="ifc:cType" fixed="list-unique"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

     <xs:element name="WAxes" nillable="true" minOccurs="0">

      <xs:complexType>

       <xs:sequence>

        <xs:element ref="ifc:IfcGridAxis" maxOccurs="unbounded"/>

       </xs:sequence>

       <xs:attribute ref="ifc:itemType" fixed="ifc:IfcGridAxis"/>

       <xs:attribute ref="ifc:cType" fixed="list-unique"/>

       <xs:attribute ref="ifc:arraySize" use="optional"/>

      </xs:complexType>

     </xs:element>

    </xs:sequence>

    <xs:attribute name="PredefinedType" type="ifc:IfcGridTypeEnum" use="optional"/>

   </xs:extension>

  </xs:complexContent>

 </xs:complexType>

EXPRESS Specification


ENTITY IfcGrid

 SUBTYPE OF (IfcPositioningElement);

  UAxes : LIST [1:?] OF UNIQUE IfcGridAxis;

  VAxes : LIST [1:?] OF UNIQUE IfcGridAxis;

  WAxes : OPTIONAL LIST [1:?] OF UNIQUE IfcGridAxis;

  PredefinedType : OPTIONAL IfcGridTypeEnum;

END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
IFC2x3 to IFC4
IfcGrid
OwnerHistory	MODIFIED	Instantiation changed to OPTIONAL.
PredefinedType	ADDED

	Raster
	Grid
	Grille

IfcGrid

Semantic definitions at the entity

Inherited definitions from supertypes

Definitions applying to General Usage

Examples

Formal representations