IfcSurface

ifc曲面是位于三维空间中的二维表示项。二维意味着曲面上的每个点都可以由二维坐标系定义，通常由u和v坐标确定。
注：定义根据ISO/CD 10303-42:1992
曲面可以想象为三维空间中的一组连通点，它通常是局部二维的，但不必是流形。
注：实体改编自ISO 10303-42中定义的表面。

IFC1.5中增加的新实体

非正式提议：
①曲面具有非零面积。
②曲面呈弧形连接。

#	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
IfcSurface
	Dim :=3	IfcDimensionCount	[1:1]	The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item.	X

EXPRESS Specification

ENTITY IfcSurface
 ABSTRACT SUPERTYPE OF(ONEOF(IfcBoundedSurface, IfcElementarySurface, IfcSweptSurface))
 SUBTYPE OF (IfcGeometricRepresentationItem);
 DERIVE
  Dim : IfcDimensionCount := 3;
END_ENTITY;