5.4.3.24 IfcGrid

Grille
Raster

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 119, a radial layout as shown in Figure 120, or a triangular layout as shown in Figure 121.

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.
1 2 3

Figure 119 — Grid rectangular layout

Figure 120 — Grid radial layout

Figure 121 — 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:

  1. Grid axes, which are referenced in different lists of axes (UAxes, VAxes, WAxes) shall not be parallel.
  2. 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.
IP2

Figure 122 — Grid intersections


Common Use Definitions

The following concepts are inherited at supertypes:

 Instance diagram

Product Placement

The Product Placement concept applies to this entity.

The local placement for IfcGrid 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.



FootPrint Geometry

The FootPrint Geometry concept applies to this entity as shown in Table 53.
IdentifierTypeItems
   

Table 53 — IfcGrid FootPrint Geometry

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

The following constraints apply to the 2D representation:

design grid
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 123 — Grid layout

 

 

representation of a design grid
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 IfcCurve (here the subtype IfcPolyline) that is contained within the IfcGeometricCurveSet that represents the IfcGrid.

Figure 124 — Grid representation

 



XSD 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;

Link to EXPRESS-G diagram EXPRESS-G diagram

Attribute Definitions:

UAxes : List of grid axes defining the first row of grid lines.
VAxes : List of grid axes defining the second row of grid lines.
WAxes : List of grid axes defining the third row of grid lines. It may be given in the case of a triangular grid.
PredefinedType : Predefined types to define the particular type of the grid.
IFC4 CHANGE  New attribute.
ContainedInStructure : 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:

HasPlacement : The placement for the grid has to be given.

Inheritance Graph:

ENTITY IfcGrid
ENTITY IfcRoot
GlobalId : IfcGloballyUniqueId;
OwnerHistory : OPTIONAL IfcOwnerHistory;
Name : OPTIONAL IfcLabel;
Description : OPTIONAL IfcText;
ENTITY IfcObjectDefinition
INVERSE
HasAssignments : SET OF IfcRelAssigns FOR RelatedObjects;
Nests : SET [0:1] OF IfcRelNests FOR RelatedObjects;
IsNestedBy : SET OF IfcRelNests FOR RelatingObject;
HasContext : SET [0:1] OF IfcRelDeclares FOR RelatedDefinitions;
IsDecomposedBy : SET OF IfcRelAggregates FOR RelatingObject;
Decomposes : SET [0:1] OF IfcRelAggregates FOR RelatedObjects;
HasAssociations : SET OF IfcRelAssociates FOR RelatedObjects;
ENTITY IfcObject
ObjectType : OPTIONAL IfcLabel;
INVERSE
IsDeclaredBy : SET [0:1] OF IfcRelDefinesByObject FOR RelatedObjects;
Declares : SET OF IfcRelDefinesByObject FOR RelatingObject;
IsTypedBy : SET [0:1] OF IfcRelDefinesByType FOR RelatedObjects;
IsDefinedBy : SET OF IfcRelDefinesByProperties FOR RelatedObjects;
ENTITY IfcProduct
ObjectPlacement : OPTIONAL IfcObjectPlacement;
Representation : OPTIONAL IfcProductRepresentation;
INVERSE
ReferencedBy : SET OF IfcRelAssignsToProduct FOR RelatingProduct;
ENTITY IfcGrid
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;
END_ENTITY;

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