IfcPolyline是一条有界曲线，只有由笛卡尔点列表定义的直线段。如果列表中的第一个和最后一个笛卡尔点相同，则多段线为闭合曲线，否则为开放曲线。
下图演示了有界IfcPolyline，并显示了每个线段和整个多段线的参数化长度。
带参数长度的有界IfcPolyline
根据注释CD-03/ISO 10342定义
多段线是由n-1条直线段组成的有界曲线，由n个点、P1、P2。。。请注意。曲线的第i段参数化如下：
式中i-1≤u≤i且参数范围为0<≤u≤n-1。
注：实体改编自ISO 10303-42中的折线。
IFC1.0中增加的新实体
Formal Propositions
| Rule | Description |
|---|---|
| SameDim | The space dimensionality of all Points shall be the same. |
| # | 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 | |
| IfcBoundedCurve | |||||
| IfcPolyline | |||||
| 1 | Points | IfcCartesianPoint | L[2:?] | The points defining the polyline. | X |
ENTITY IfcPolyline SUBTYPE OF (IfcBoundedCurve); Points : LIST [2:?] OF IfcCartesianPoint; WHERE SameDim : SIZEOF(QUERY(Temp <* Points | Temp.Dim <> Points[1].Dim)) = 0; END_ENTITY;
原文：https://www.cnblogs.com/herd/p/13253596.html