IfcPlacement

IfcPlacement是放置子类型的抽象超类型，定义项或整个形状表示的位置并提供其方向。所有放置子类型都定义右手笛卡尔坐标系，不允许镜像。

注意笛卡尔变换（包括镜像和缩放）受IfcCartesianTransformationOperator支持

注：定义根据ISO/CD 10303-42:1992

放置相对于其几何上下文的坐标系定位几何项。它定位要定义的项，并在轴放置子类型的情况下给出其方向。

注：实体改编自ISO 10303-42中定义的位置。

IFC1.0中增加的新实体

#	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

EXPRESS Specification

ENTITY IfcPlacement
 ABSTRACT SUPERTYPE OF(ONEOF(IfcAxis1Placement, IfcAxis2Placement2D, IfcAxis2Placement3D))
 SUBTYPE OF (IfcGeometricRepresentationItem);
  Location : IfcCartesianPoint;
 DERIVE
  Dim : IfcDimensionCount := Location.Dim;
END_ENTITY;