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 115, a radial layout as shown in Figure 116, or a triangular layout as shown in Figure 117.

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 115 — Grid rectangular layout	Figure 116 — Grid radial layout	Figure 117 — 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 118 — Grid intersections

Attribute definitions

#	Attribute	Type	Cardinality	Description	R
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
	ContainedInStructure	IfcRelContainedInSpatialStructure @RelatedElements	S[0:1]	Relationship to a spatial structure element, to which the grid is primarily associated. IFC2x CHANGE The inverse relationship has been added to IfcGrid with upward compatibility

Formal Propositions

Rule	Description
HasPlacement	The placement for the grid has to be given.

Inherited definitions from supertypes

Entity inheritance

Attribute inheritance

#	Attribute	Type	Cardinality	Description	R
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.
	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.
	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
	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
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
	ContainedInStructure	IfcRelContainedInSpatialStructure @RelatedElements	S[0:1]	Relationship to a spatial structure element, to which the grid is primarily associated. IFC2x CHANGE The inverse relationship has been added to IfcGrid with upward compatibility

Definitions applying to Reference View

Instance diagram

Concept usage

Grid Attributes

The Grid Attributes concept applies to this entity.

Product Local Placement

The Product Local Placement concept applies to this entity.

FootPrint GeomSet Geometry

The FootPrint GeomSet Geometry concept applies to this entity.

The 2D geometric representation of IfcGrid is defined using the 'GeometricCurveSet' geometry. The following attribute values should be inserted

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

The following constraints apply to the 2D representation:

The IfcGeometricCurveSet shall be an (and the only) Item of the IfcShapeRepresentation. It should contain an IfcGeometricCurveSet containing subtypes of IfcCurve, each representing a grid axis. Applicable subtypes of IfcCurve are: IfcPolyline, IfcCircle, IfcTrimmedCurve (based on BaseCurve referencing IfcLine or IfcCircle), and IfcOffsetCurve2D.
Each subtype of IfcCurve may have a curve style assigned, using IfcStyledItem referencing IfcCurveStyle.
Optionally the grid axis labels may be added as IfcTextLiteral, and they may have text styles assigned, using IfcStyledItem referencing IfcTextStyle.

As shown in Figure 31, the IfcGrid defines a placement coordinate system using the ObjectPlacement. The XY plane of the coordinate system is used to place the 2D grid axes. The Representation of IfcGrid is defined using IfcProductRepresentation, referencing an IfcShapeRepresentation, that includes IfcGeometricCurveSet as Items. All grid axes are added as IfcPolyline to the IfcGeometricCurveSet.

Figure 117 — Grid layout

	As shown in Figure 32, the attributes UAxes and VAxes define lists of IfcGridAxis within the context of the grid. Each instance of IfcGridAxis refers to the same instance of IfcGridAxis refers to the same instance of IfcCurve (here the subtype IfcPolyline) that is contained within the IfcGeometricCurveSet that represents theIfcGrid.
Figure 118 — Grid representation

Spatial Containment

The Spatial Containment concept applies to this entity.

mvdXML Specification


<?xml version="1.0"?>

<ConceptRoot xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" uuid="280bbb91-3d77-4b73-88d5-594762c1989d" name="IfcGrid" status="sample" applicableRootEntity="IfcGrid">

  <Applicability uuid="00000000-0000-0000-0000-000000000000" status="sample">

    <Template ref="42a17faa-bd1e-4445-970a-a7743b3a1fbf" />

    <TemplateRules operator="and" />

  </Applicability>

  <Concepts>

    <Concept uuid="3d02a39c-105e-4e15-95de-d8315e28c9c9" name="Grid Attributes" status="sample" override="false">

      <Template ref="9c7b470d-978a-40fa-a777-449b40588800" />

    </Concept>

    <Concept uuid="8634309c-d5a5-4dc6-b825-c39231ed1741" name="Product Local Placement" status="sample" override="false">

      <Template ref="cbe85b5f-7912-4a43-8bb7-1e63bf40b26d" />

    </Concept>

    <Concept uuid="f036530f-76d6-4ec0-9040-b20a00f0537f" name="FootPrint GeomSet Geometry" status="sample" override="false">

      <Template ref="9456d6d6-a62a-48b4-baff-be2e38baac9c" />

    </Concept>

    <Concept uuid="24fb04df-c6ef-41e2-afee-157b0270e9f9" name="Spatial Containment" status="sample" override="false">

      <Template ref="d9a3f822-0014-4bc2-8d94-9d9067759045" />

    </Concept>

  </Concepts>

</ConceptRoot>

Concept inheritance

#	Concept	Template	Model View
IfcRoot
	Identity	Software Identity	Reference View
	Revision Control	Revision Control	Reference View
IfcObjectDefinition
	Classification	Classification	Reference View
IfcObject
	Object User Identity	Object User Identity	Reference View
	Object Predefined Type	Object Predefined Type	Reference View
	Object Typing	Object Typing	Reference View
	Property Sets for Objects	Property Sets with Override	Reference View
IfcGrid
	Grid Attributes	Grid Attributes	Reference View
	Product Local Placement	Product Local Placement	Reference View
	FootPrint GeomSet Geometry	FootPrint GeomSet Geometry	Reference View
	Spatial Containment	Spatial Containment	Reference View

Formal representations

XML Specification

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

 <xs:complexType name="IfcGrid">

  <xs:complexContent>

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

    <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 (IfcProduct);

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

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

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

  PredefinedType : OPTIONAL IfcGridTypeEnum;

 INVERSE

  ContainedInStructure : SET [0:1] OF IfcRelContainedInSpatialStructure FOR RelatedElements;

 WHERE

  HasPlacement : EXISTS(SELF\IfcProduct.ObjectPlacement);
END_ENTITY;

 EXPRESS-G diagram

Item	Change	Description
4.0.0.0
IfcGrid
OwnerHistory	MODIFIED	Instantiation changed to OPTIONAL.
PredefinedType	ADDED

	Raster
	Grid
	Grille