IFC 4.3.x development

8.14.3.7 IfcLightSourcePositional

8.14.3.7.1 Semantic definitions at the entity

NOTE  Definition according to ISO 10303-46:
The light source positional entity is a subtype of light source. This entity has a light source position and attenuation coefficients. A positional light source affects a surface based on the surface's orientation and position.

NOTE  Definition according to ISO/IEC 14772-1:1997:
The Point light node specifies a point light source at a 3D location in the local coordinate system. A point light source emits light equally in all directions; that is, it is omnidirectional. Point light nodes are specified in the local coordinate system and are affected by ancestor transformations.

Point light node's illumination falls off with distance as specified by three attenuation coefficients. The attenuation factor is

1/max(attenuation[0] + attenuation[1] × r + attenuation[2] × r 2 , 1), where r is the distance from the light to the surface being illuminated. The default is no attenuation. An attenuation value of (0, 0, 0) is identical to (1, 0, 0). Attenuation values shall be greater than or equal to zero.

NOTE  Corresponding ISO 10303 entity: light_source_positional. Please refer to ISO/IS 10303-46:1994, p. 32 for the final definition of the formal standard.

NOTE  In addition to the attributes as defined in ISO10303-46 the additional property from ISO/IEC 14772-1:1997 (VRML) Radius and QuadricAttenuation are added to this subtype and the AmbientIntensity and Intensity are inherited from the supertype.

HISTORY  New entity in IFC2x, renamed and enhanced in IFC2x2.

8.14.3.7.1 Attributes

# Attribute Type Description
IfcRepresentationItem
LayerAssignment SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItemsAssignment 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.

> IFC2x3 CHANGE  The inverse attribute LayerAssignments has been added.

> IFC4 CHANGE  The inverse attribute LayerAssignment has been restricted to max 1. Upward compatibility for file based exchange is guaranteed.
StyledByItem SET [0:1] OF IfcStyledItem FOR Item Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.



> IFC2x3 CHANGE  The inverse attribute StyledByItem has been added.
IfcGeometricRepresentationItem
IfcLightSource
1 Name OPTIONAL IfcLabel The name given to the light source in presentation.
2 LightColour IfcColourRgb 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.
3 AmbientIntensity OPTIONAL IfcNormalisedRatioMeasure 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).
4 Intensity OPTIONAL IfcNormalisedRatioMeasure 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).
IfcLightSourcePositional
5 Position IfcCartesianPoint 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.
6 Radius IfcPositiveLengthMeasure 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.
7 ConstantAttenuationIfcReal Definition from ISO/CD 10303-46:1992: This real indicates the value of the attenuation in the lighting equation that is constant.
8 DistanceAttenuationIfcReal 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.
9 QuadricAttenuation IfcReal 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.

8.14.3.7.2 Entity inheritance

dot_inheritance IfcLightSourceSpot IfcLightSourceSpot IfcLightSourcePositional IfcLightSourcePositional IfcLightSourceSpot->IfcLightSourcePositional IfcLightSource IfcLightSource IfcLightSourcePositional->IfcLightSource IfcLightSource_children 3 more... IfcLightSource_children->IfcLightSource IfcGeometricRepresentationItem IfcGeometricRepresentationItem IfcLightSource->IfcGeometricRepresentationItem IfcGeometricRepresentationItem_children 24 more... IfcGeometricRepresentationItem_children->IfcGeometricRepresentationItem IfcRepresentationItem IfcRepresentationItem IfcGeometricRepresentationItem->IfcRepresentationItem IfcRepresentationItem_children 3 more... IfcRepresentationItem_children->IfcRepresentationItem

8.14.3.7.3 Formal representations

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