IfcEllipse

时间：2020-07-09 23:46:24 阅读：68 评论：0 收藏：0 [点我收藏+]

IfcEllipse是一条由一组点组成的曲线，这些点到两个固定点的距离加上同一个常数。

遗传的自我\IfcConic.Position.位置是IfcEllipse的中心，也是遗传的自我\IfcConic.Position.位置.P[1]是半轴的方向1。

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下图显示了在三维位置坐标系中的IfcEllipse的定义。

它被放置在其表示元素的对象坐标系中。

注：椭圆弧段是通过使用带BasisCurve的IfcTrimmedCurve定义的

注：定义根据ISO/CD 10303-42:1992

椭圆是由半大径和半小径的长度以及曲线的位置（连接焦点的直线的中心或中点）和方向定义的圆锥截面。数据解释如下：

C = position.location
x = position.p[1]
y = position.p[2]
z = position.p[3]
R1 = semi axis 1
R2 = semi axis 2

椭圆参数化为：

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参数化范围为0≤u<≤2π（0≤u≤360度）。在上面定义的放置坐标系中，椭圆是方程C=0，其中

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椭圆在任何一点的正方向都是在切线方向，T，与曲线在该点，其中

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注：实体改编自ISO 10303-42中定义的椭圆

IFC1.0中增加的新实体

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#	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
IfcConic
1	Position	IfcAxis2Placement	[1:1]	The location and orientation of the conic. Further details of the interpretation of this attribute are given for the individual subtypes."	X
IfcEllipse
2	SemiAxis1	IfcPositiveLengthMeasure	[1:1]	The first radius of the ellipse which shall be positive. Placement.Axes[1] gives the direction of the SemiAxis1.	X
3	SemiAxis2	IfcPositiveLengthMeasure	[1:1]	The second radius of the ellipse which shall be positive.	X

ENTITY IfcEllipse
 SUBTYPE OF (IfcConic);
  SemiAxis1 : IfcPositiveLengthMeasure;
  SemiAxis2 : IfcPositiveLengthMeasure;
END_ENTITY;

原文：https://www.cnblogs.com/herd/p/13276704.html

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