ifcaxis1位置提供单个轴的位置和方向。
图说明了ifcaxis1在父三维坐标系中的位置的定义。
注：定义根据ISO/CD 10303-42:1992
单轴在三维空间中的方向和位置。axis1_放置是根据定位点（从placement supertype继承）和轴方向定义的：这是轴的方向，或者默认为（0.0,0.0,1.0）。轴放置的实际方向由派生属性z给出。
注：实体改编自ISO10303-42中定义的axis1_位置。
IFC1.5中增加的新实体
Formal Propositions
| Rule | Description |
|---|---|
| AxisIs3D | The Axis when given should only reference a three-dimensional IfcDirection. |
| LocationIs3D | The Cartesian point defining the Location shall have the dimensionality of 3. |
| # | Attribute | Type | Cardinality | Description | C |
|---|---|---|---|---|---|
| IfcRepresentationItem | |||||
| LayerAssignment | IfcPresentationLayerAssignment @AssignedItems |
S[0:1] | Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items. | X | |
| StyledByItem | IfcStyledItem @Item |
S[0:1] | Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. | X | |
| IfcGeometricRepresentationItem | |||||
| IfcPlacement | |||||
| 1 | Location | IfcCartesianPoint | [1:1] | The geometric position of a reference point, such as the center of a circle, of the item to be located. | X |
| Dim :=Location.Dim |
IfcDimensionCount | [1:1] | The space dimensionality of this class, derived from the dimensionality of the location. | X | |
| IfcAxis1Placement | |||||
| 2 | Axis | IfcDirection | [0:1] | The direction of the local Z axis. | X |
| Z :=NVL (IfcNormalise(Axis), IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcDirection([0.0,0.0,1.0])) |
IfcDirection | [1:1] | The normalized direction of the local Z axis. It is either identical with the Axis value, if given, or it defaults to [0.,0.,1.] | X | |
ENTITY IfcAxis1Placement
SUBTYPE OF (IfcPlacement);
Axis : OPTIONAL IfcDirection;
DERIVE
Z : IfcDirection := NVL (IfcNormalise(Axis), IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcDirection([0.0,0.0,1.0]));
WHERE
AxisIs3D : (NOT (EXISTS (Axis))) OR (Axis.Dim = 3);
LocationIs3D : SELF\IfcPlacement.Location.Dim = 3;
END_ENTITY;
原文：https://www.cnblogs.com/herd/p/13415765.html