IfcAxis2Placement3D

IfcAxis2Placement3D提供在三维空间中放置项目的位置和方向。属性轴定义Z方向，RefDirection定义X方向。导出Y方向。

注：参照方向不必与轴正交。

如果未给出Axis和RefDirection的属性值，则放置默认为P[1]（x轴）为[1,0,0.]，P[2]（y轴）为[0,1,0.]，P[3]（z轴）为[0,0,1]。

图说明了三维坐标系中IfcAxis2Placement3D的定义。

注：定义根据ISO/CD 10303-42:1992

三个相互垂直的轴在三维空间中的位置和方向。axis2_placement_3D是根据一个点（继承自placement supertype）和两个（理想的正交）轴定义的。它可以用于空间中非轴对称物体的定位和定向，以及确定放置坐标系。图元包括形成放置坐标系原点的点。需要两个方向向量来完成放置坐标系的定义。轴是放置Z轴的方向，ref_方向是放置X轴方向的近似值。

注：实体改编自ISO10303-42中定义的axis2_placement_3d。

在IFC1.5中增加的新实体。

Formal Propositions

Rule	Description
LocationIs3D	The dimensionality of the placement location shall be 3.
AxisIs3D	The Axis when given should only reference a three-dimensional IfcDirection.
RefDirIs3D	The RefDirection when given should only reference a three-dimensional IfcDirection.
AxisToRefDirPosition	The Axis and RefDirection shall not be parallel or anti-parallel.
AxisAndRefDirProvision	Either both, Axis and RefDirection are not given and therefore defaulted, or both shall be given.

 

Attribute inheritance

#	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
IfcAxis2Placement3D
2	Axis	IfcDirection	[0:1]	The exact direction of the local Z Axis.	X
3	RefDirection	IfcDirection	[0:1]	The direction used to determine the direction of the local X Axis. If necessary an adjustment is made to maintain orthogonality to the Axis direction. If Axis and/or RefDirection is omitted, these directions are taken from the geometric coordinate system.	X
	P :=IfcBuildAxes(Axis, RefDirection)	IfcDirection	L[3:3]	The normalized directions of the placement X Axis (P[1]) and the placement Y Axis (P[2]) and the placement Z Axis (P[3]).	X

 

EXPRESS Specification

ENTITY IfcAxis2Placement3D
 SUBTYPE OF (IfcPlacement);
  Axis : OPTIONAL IfcDirection;
  RefDirection : OPTIONAL IfcDirection;
 DERIVE
  P : LIST [3:3] OF IfcDirection := IfcBuildAxes(Axis, RefDirection);
 WHERE
  LocationIs3D : SELFIfcPlacement.Location.Dim = 3;
  AxisIs3D : (NOT (EXISTS (Axis))) OR (Axis.Dim = 3);
  RefDirIs3D : (NOT (EXISTS (RefDirection))) OR (RefDirection.Dim = 3);
  AxisToRefDirPosition : (NOT (EXISTS (Axis))) OR (NOT (EXISTS (RefDirection))) OR (IfcCrossProduct(Axis,RefDirection).Magnitude > 0.0);
  AxisAndRefDirProvision : NOT ((EXISTS (Axis)) XOR (EXISTS (RefDirection)));
END_ENTITY;