IfcLightSourcePositional

注：根据ISO 10303-46的定义：

光源位置实体是光源的子类型。此实体具有光源位置和衰减系数。位置光源基于曲面的方向和位置影响曲面。

注：根据ISO/IEC 14772-1:1997的定义：

“点光源”节点在局部坐标系中的三维位置指定点光源。点光源在所有方向上均匀地发射光；也就是说，它是全向的。点光源节点在局部坐标系中指定，并受祖先变换的影响。

点光源节点的照明随距离衰减，由三个衰减系数指定。衰减系数为

1/max（衰减[0]+衰减[1]×r+衰减[2]×r2，1），

式中，r是从灯光到被照明表面的距离。默认设置为“无衰减”。衰减值（0，0，0）与（1，0，0）相同。衰减值应大于或等于零。

注：对应的ISO 10303实体：光源位置。有关正式标准的最终定义，请参考ISO/IS 10303-46:1994，第32页。

注：除ISO10303-46中定义的属性外，ISO/IEC 14772-1:1997（VRML）半径和四边形的附加属性添加到该子类型中，模糊度和强度从父类型继承。

IFC2x中增加的新实体，在IFC2x2中重命名和增强。

#	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
IfcLightSource
1	Name	IfcLabel	[0:1]	The name given to the light source in presentation.	X
2	LightColour	IfcColourRgb	[1:1]	Definition from ISO/CD 10303-46:1992: Based on the current lighting model, the colour of the light to be used for shading. Definition from VRML97 - ISO/IEC 14772-1:1997: The color field specifies the spectral color properties of both the direct and ambient light emission as an RGB value.	X
3	AmbientIntensity	IfcNormalisedRatioMeasure	[0:1]	Definition from VRML97 - ISO/IEC 14772-1:1997: The ambientIntensity specifies the intensity of the ambient emission from the light. Light intensity may range from 0.0 (no light emission) to 1.0 (full intensity).	X
4	Intensity	IfcNormalisedRatioMeasure	[0:1]	Definition from VRML97 - ISO/IEC 14772-1:1997: The intensity field specifies the brightness of the direct emission from the ligth. Light intensity may range from 0.0 (no light emission) to 1.0 (full intensity).	X
IfcLightSourcePositional
5	Position	IfcCartesianPoint	[1:1]	Definition from ISO/CD 10303-46:1992: The Cartesian point indicates the position of the light source. Definition from VRML97 - ISO/IEC 14772-1:1997: A Point light node illuminates geometry within radius of its location.	X
6	Radius	IfcPositiveLengthMeasure	[1:1]	The maximum distance from the light source for a surface still to be illuminated. Definition from VRML97 - ISO/IEC 14772-1:1997: A Point light node illuminates geometry within radius of its location.	X
7	ConstantAttenuation	IfcReal	[1:1]	Definition from ISO/CD 10303-46:1992: This real indicates the value of the attenuation in the lighting equation that is constant.	X
8	DistanceAttenuation	IfcReal	[1:1]	Definition from ISO/CD 10303-46:1992: This real indicates the value of the attenuation in the lighting equation that proportional to the distance from the light source.	X
9	QuadricAttenuation	IfcReal	[1:1]	This real indicates the value of the attenuation in the lighting equation that proportional to the square value of the distance from the light source.	X

EXPRESS Specification

ENTITY IfcLightSourcePositional
 SUPERTYPE OF(IfcLightSourceSpot)
 SUBTYPE OF (IfcLightSource);
  Position : IfcCartesianPoint;
  Radius : IfcPositiveLengthMeasure;
  ConstantAttenuation : IfcReal;
  DistanceAttenuation : IfcReal;
  QuadricAttenuation : IfcReal;
END_ENTITY;