Class Name: Positional Light

Superclass - <Base Positional Light>

Subclasses

Definition

An instance of this DRM class is a <Base Positional Light> instance that radiates in all directions from a specified point in 3D space, affecting only objects within the sphere of influence centred at that point and specified by the value of its radius field.

Primary Page in DRM Diagram:

• 21

Secondary Pages in DRM Diagram:

Example

1. A <Positional Light> instance represents streetlight on a pole.

FAQs

No FAQs supplied.

Constraints

• <<Publishable Object>>
• <<Inheritance Rule For Location>>

Composed of (two-way) (inherited)

• one <Ambient Colour> instance
• zero or one <Classification Data> instance¹
• one <Diffuse Colour> instance
• zero or one <Light Source Control Link> instance²
• one <Specular Colour> instance
• one <Location 3D> instance³

Component of (two-way) (inherited)

• one or more <Aggregate Geometry> instances

Inherited Field Elements

Notes

Composed of Notes

Classification_Data

Light_Source_Control_Link

Location_3D

Fields Notes

apply_to_children

For a <Light Source> instance that is a component of some <Aggregate Geometry> instance(s), apply_to_children provides a mechanism for limiting the scope of the <Light Source> instance. If apply_to_children is SE_TRUE, only <Primitive Geometry> instances in the component tree of those <Aggregate Geometry> instances are affected by the <Light Source> instance. If apply_to_children is SE_FALSE, the <Light Source> instance is not limited to the scope of those <Aggregate Geometry> instances and thus applies globally.

override_positional_lights

For a <Light Source> instance that is a component of some <Aggregate Geometry> instance, override_positional_lights provides a mechanism to indicate with a value of SE_TRUE that the effect of the <Light Source> instance overrides that of any <Base Positional Light> instances that would have otherwise applied to that <Aggregate Geometry> instance.

EXAMPLE  This might be appropriate if the <Light Source> instance is so close to the affected <Geometry Representation> instance(s) that the effects of the <Base Positional Light> instances would be negligible.

If override_positional_lights = SE_FALSE, the effect of the <Light Source> instance is combined with that of any <Base Positional Light> instances that are already in effect.

override_infinite_lights

For a <Light Source> instance that is a component of some <Aggregate Geometry> instance, override_infinite_lights provides a mechanism to indicate with a value of SE_TRUE that the effect of the <Light Source> instance overrides that of any <Infinite Light> instances that would have otherwise applied to that <Aggregate Geometry> instance. If override_infinite_lights = SE_FALSE, the effect of the <Light Source> instance is combined with that of any <Infinite Light> instances that are already in effect.

active_light_value

A value of SE_TRUE for the active_light_value field indicates that the light is on, while a value of SE_FALSE indicates that the light is off. For a <Light Source> instance with a <Light Source Control Link> component X, the value of the active_light_value field is obtained from X.

radius

The radius field, which is specified in metres, together with the <Location 3D> component specifies the zone of influence of the <Base Positional Light> instance.

constant_attenuation_factor

The constant_attenuation_factor field is the constant "a" in the attenuation quadratic (a + bd + cd²).

linear_attenuation_factor

The linear_attenuation_factor field is the constant "b" in the attenuation quadratic (a + bd + cd²).

quadratic_attenuation_factor

The quadratic_attenuation_factor field is the constant "c" in the attenuation quadratic (a + bd + cd²).