IfcVector

IfcVector是一个既有大小又有方向的几何表示项。矢量的大小仅由“幅值”属性定义，方向仅由“方向”属性定义。

注意“方向”属性的“方向比率”不用于定义幅值。

注：定义根据ISO/CD 10303-42:1992

矢量是根据矢量的方向和大小定义的。“幅值”属性的值定义向量的幅值。从方向属性的分量计算矢量的大小是不可靠的。选择这种表示形式是为了减少数值不稳定的问题。例如，大小为2.0 mm且与坐标轴相等倾斜的向量可以用方向属性（1.0,1.0,1.0）表示。

注：实体改编自ISO 10303-42中定义的矢量。

IFC1.0中增加的新实体

Formal Propositions

Rule	Description
MagGreaterOrEqualZero	The magnitude shall be positive or zero.

 

#	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
IfcVector
1	Orientation	IfcDirection	[1:1]	The direction of the vector.	X
2	Magnitude	IfcLengthMeasure	[1:1]	The magnitude of the vector. All vectors of Magnitude 0.0 are regarded as equal in value regardless of the orientation attribute.	X
	Dim :=Orientation.Dim	IfcDimensionCount	[1:1]	The space dimensionality of this class, it is derived from Orientation	X

 

EXPRESS Specification

ENTITY IfcVector
 SUBTYPE OF (IfcGeometricRepresentationItem);
  Orientation : IfcDirection;
  Magnitude : IfcLengthMeasure;
 DERIVE
  Dim : IfcDimensionCount := Orientation.Dim;
 WHERE
  MagGreaterOrEqualZero : Magnitude >= 0.0;
END_ENTITY;