#### 5.4.2.1 IfcGridTypeEnum

This enumeration defines the different layout types of grids. Restriction on the correct use of IfcGrid instantiations may be imposed depending on the value of the PredefinedType being IfcGridTypeEnum.

> HISTORY New enumeration in IFC4.

Enumeration:

- RECTANGULAR: an IfcGrid with straight u-axes and straight v-axes being perpendicular to each other. All grid axes being part of u-axes can be described by one axis line and all other axes being 2D offsets from this axis line. The same applies to all grid axes being part of V-axes.
- RADIAL: an IfcGrid with straight u-axes and curved v-axes. All grid axes being part of V-axes have the same center point and are concentric circular arcs. All grid axes being part of u-axes intersect at the same center point and rotate counter clockwise.
- TRIANGULAR: an IfcGrid with u-axes, v-axes, and w-axes all being co-linear axis lines with a 2D offset. The v-axes are at 60 degree rotated counter clockwise from the u-axes, and the w-axes are at 120 degree rotated counter clockwise from the u-axes.
- IRREGULAR: an IfcGrid with u-axes, v-axes, and optionally w-axes that cannot be described by the patterns RECTANGULAR, RADIAL, TRIANGULAR.

  > NOTE Grids with irregular offsets between parallel or cocentric grid axes are not considered as IRREGULAR if they otherwise meet the criteria of RECTANGULAR, RADIAL, TRIANGULAR

- USERDEFINED: any other grid not conforming to any of the above restrictions;
- NOTDEFINED: not known whether grid conforms to any standard type.

> NOTE View definitions or implementer agreements may impose further restrictions on how to populate the grid axes. The first grid axis being part of u-axes may have to be parallel to the x-axis of the grid object placement.

XSD Specification:

<xs:simpleType name="IfcGridTypeEnum">
<xs:restriction base="xs:string">
<xs:enumeration value="rectangular"/>
<xs:enumeration value="radial"/>
<xs:enumeration value="triangular"/>
<xs:enumeration value="irregular"/>
<xs:enumeration value="userdefined"/>
<xs:enumeration value="notdefined"/>
</xs:restriction>
</xs:simpleType>

EXPRESS Specification:

TYPE IfcGridTypeEnum = ENUMERATION OF (
| RECTANGULAR, RADIAL, TRIANGULAR, IRREGULAR, USERDEFINED, NOTDEFINED);
END_TYPE;

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