IfcLine

IfcLine是由IfcCartesianPoint和IfcVector参数化的无界线。IfcVector的大小会影响线的参数化，但不会绑定线。

注：线段是使用带两点的IfcPolyline或BasisCurve为IfcLine的IfcTrimmedCurve定义的。

下图演示了一个无界IfcLine和一个有界ifctrimedcurve。从0，0开始的有界线。在0，2结束。可定义为：

①如果与IfcVector.震级：2.0和带微调1:0的IfcTrimmedCurve。修剪2:1。参数和微调；

②如果与IfcVector.震级：1.0和带微调1:0的IfcTrimmedCurve。修剪2:2。参数和微调；

③笛卡儿切边2，和切边切边2IfcVector.震级没有效果；

④点[1]为0,0的多边形。点[2]为0,2。

——无界IfcLine与有界ifcTrimedCurve

注：定义根据ISO/CD 10303-42:1992

直线是一条切线方向不变的无界曲线。直线由点和方向定义。直线的正方向是dir向量的方向。曲线参数化如下：

P = Pnt
V = Dir
λ(u) = P + uV

参数范围为：

 -∞ < u < ∞

注：实体改编自ISO 10303-42中定义的线

IFC1.0中增加的新实体

Formal Propositions

Rule	Description
SameDim	The dimensionality of the Pnt, provided by IfcCartesianPoint, shall be the same as the dimensionality of the Dir, provided by IfcVector.

 

#	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
IfcCurve
	Dim :=IfcCurveDim(SELF)	IfcDimensionCount	[1:1]	The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.	X
IfcLine
1	Pnt	IfcCartesianPoint	[1:1]	The location of the IfcLine.	X
2	Dir	IfcVector	[1:1]	The direction of the IfcLine, the magnitude and units of Dir affect the parameterization of the line.	X

EXPRESS Specification

ENTITY IfcLine
 SUBTYPE OF (IfcCurve);
  Pnt : IfcCartesianPoint;
  Dir : IfcVector;
 WHERE
  SameDim : Dir.Dim = Pnt.Dim;
END_ENTITY;