IfcDirection

ifc方向提供二维或三维空间中的方向，具体取决于所提供的方向比率的数量。ifc方向并不意味着矢量长度，方向比也不必标准化。

注：定义根据ISO/CD 10303-42:1992

此实体定义二维或三维空间中的一般方向向量。分量的实际大小对定义的方向没有影响，只有X:Y:Z或X:Y的比值才有意义。

请注意，此实体的组件未规范化。如果需要单位矢量，则应在使用前对其进行规范化。

注：实体改编自ISO 10303-42中定义的方向。

IFC1.0中增加的新实体

Formal Propositions

Rule	Description
MagnitudeGreaterZero	The magnitude of the direction vector shall be greater than 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
IfcDirection
1	DirectionRatios	IfcReal	L[2:3]	The components in the direction of X axis (DirectionRatios[1]), of Y axis (DirectionRatios[2]), and of Z axis (DirectionRatios[3])	X
	Dim :=HIINDEX(DirectionRatios)	IfcDimensionCount	[1:1]	The space dimensionality of this class, defined by the number of real in the list of DirectionRatios.	X

EXPRESS Specification

ENTITY IfcDirection
 SUBTYPE OF (IfcGeometricRepresentationItem);
  DirectionRatios : LIST [2:3] OF IfcReal;
 DERIVE
  Dim : IfcDimensionCount := HIINDEX(DirectionRatios);
 WHERE
  MagnitudeGreaterZero : SIZEOF(QUERY(Tmp <* DirectionRatios | Tmp <> 0.0)) > 0;
END_ENTITY;