标签：table 不同 reference edit detail tab rri car geo
IfcOffsetCurve3D是由三维空间中与其基本曲率的偏移量定义的曲线。
注：定义根据ISO/CD 10303-42:1992
偏移曲线3d是三维空间中与基本曲线保持恒定距离的曲线。基础曲线应在每个点处具有明确的切线方向。在复合曲线的情况下，每段之间的过渡代码应为连续相同坡度或相同坡度相同曲率。基准曲线上任何点（参数）的偏移曲线在V x T方向，其中V是固定的参考方向，T是与基准曲线相切的单位。对于要明确定义的偏移方向，T不得在曲线的任何点与V方向相同或相反。
注：偏移曲线3d在性质上可能不同于基准曲线；非自相交曲线的偏移可以是自相交的。应注意确保连续曲线的偏移不会变得不连续。
偏移曲线3d从基础曲线获取其参数化。偏移曲线3d参数化为：
T是参数值u处基本曲线C（u）的单位切线向量，d是距离。基础曲线应为三维曲线。
注：实体改编自ISO 10303-42中定义的偏移曲线_3d
IFC2x中增加的新实体
非正式提议：
在曲线上的任何点上，ref方向不得与切线向量的方向平行或相反。
Formal Propositions
| Rule | Description |
|---|---|
| DimIs2D | The underlying curve shall be defined in three-dimensional space. |
| # | 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 | |
| IfcOffsetCurve3D | |||||
| 1 | BasisCurve | IfcCurve | [1:1] | The curve that is being offset. | X |
| 2 | Distance | IfcLengthMeasure | [1:1] | The distance of the offset curve from the basis curve. The distance may be positive, negative or zero. | X |
| 3 | SelfIntersect | IfcLogical | [1:1] | An indication of whether the offset curve self-intersects, this is for information only. | X |
| 4 | RefDirection | IfcDirection | [1:1] | The direction used to define the direction of the offset curve 3d from the basis curve. | X |
ENTITY IfcOffsetCurve3D
SUBTYPE OF (IfcCurve);
BasisCurve : IfcCurve;
Distance : IfcLengthMeasure;
SelfIntersect : IfcLogical;
RefDirection : IfcDirection;
WHERE
DimIs2D : BasisCurve.Dim = 3;
END_ENTITY;
标签：table 不同 reference edit detail tab rri car geo
原文地址：https://www.cnblogs.com/herd/p/13288516.html
