An individual axis, IfcGridAxis, is defined in the context of a design grid. The axis definition is based on a curve of dimensionality 2. The grid axis is positioned within the XY plane of the position coordinate system defined by the IfcGrid.

The standard geometric representation of IfcGridAxis is defined using a 2D curve entity. Grid axes are normally defined by an offset to another axis. The IfcOffsetCurve2D supports this concept. Each grid axis has a sense given by the parameterization of the curve. The attribute SameSense is an indicator of whether or not the sense of the grid axis agrees with, or opposes, that of the underlying curve.

As shown in Figure 1, the grid axis is defined as a 2D curve within
the xy plane of the position coordinate system. Any curve can be
used to define a grid axis, most common is the use of IfcLine for
linear grids and IfcCircle for radial grids.

Most grids are defined by a pair of axis
lists, each defined by a base grid axis and axes given by an
offset to the base axis. The use of IfcOffsetCurve2D as
underlying AxisCurve supports this concept.

The reference to a set of > IFC2x3 CHANGE New inverse attribute.

8.7.3.11.2 Entity inheritance

8.7.3.11.3 Formal representations

ENTITY IfcGridAxis;
AxisTag : OPTIONAL IfcLabel;
AxisCurve : IfcCurve;
SameSense : IfcBoolean;
INVERSE
PartOfW : SET [0:1] OF IfcGrid FOR WAxes;
PartOfV : SET [0:1] OF IfcGrid FOR VAxes;
PartOfU : SET [0:1] OF IfcGrid FOR UAxes;
HasIntersections : SET [0:?] OF IfcVirtualGridIntersection FOR IntersectingAxes;
WHERE
WR1 : AxisCurve.Dim = 2;
WR2 : (SIZEOF(PartOfU) = 1) XOR (SIZEOF(PartOfV) = 1) XOR (SIZEOF(PartOfW) = 1);
END_ENTITY;