Class

• <DRM Spot Light>

Superclass

• <DRM Base Positional Light>

Subclass

• None.

Definition

An instance of this DRM class is a <DRM Base Positional Light> instance that specifies an elliptic cone of influence, the tip of which is the specified <DRM Location 3D> component. The cone is bounded where it intersects the sphere centred at the tip, the radius of which is given by the radius field. This results in a a cone-shaped volume of influence, possibly smashed in one direction. Only objects located within this cone can be affected.

The intensity dropoff is computed as follows:

Given a point on a ray in the cone at fixed distance D from the cone apex, if :

I₀ is the intensity on the <DRM Lobe Data> direction axis at distance D
A_h is the horizontal angle of the ray in degrees from direction vector
A_v is the vertical angle of the ray in degrees from direction vector

the intensity I at the point is computed as follows:

case:  0.0 < horizontal_drop_off_rate, 0.0 < vertical_drop_off_rate

I = I₀ × (1.0 - |A_h| × horizontal_drop_off_rate)
    × (1.0 - |A_v| × vertical_drop_off_rate)

case:  0.0 = horizontal_drop_off_rate, 0.0 < vertical_drop_off_rate

I = I₀ × (1.0 - |A_v| × vertical_drop_off_rate)

case:  0.0 < horizontal_drop_off_rate, 0.0 = vertical_drop_off_rate

I = I₀ × (1.0 - |A_h| × horizontal_drop_off_rate)

The horizontal_drop_off_rate specifies, in radians, the horizontal angular intensity distribution of the light. The higher this value, the more focused the light. A value of 0,0 specifies a light that equally illuminates all objects within the cone of influence, and instantly falls to an intensity of 0,0 at the edge of the cone of light.

The vertical_drop_off_rate specifies, in radians, the vertical angular intensity distribution of the light. The higher this value, the more focused the light. A value of 0,0 specifies a light that equally illuminates all objects within the cone of influence, and instantly falls to an intensity of 0,0 at the edge of the cone of light.

Class diagram

Figure 6.305 — DRM_Spot_Light

Constraints

• Publishable Object

Example(s)

• A <DRM Model> instance of a lighthouse has a <DRM Geometry Model> instance with a <DRM Union Of Geometry Hierarchy> instance, to which is attached an <DRM Spot Light> instance representing the lighthouse light. The <DRM Spot Light> instance has a <DRM Light Source Control Link> instance that turns the light on or off, depending on the time of day and the weather.

• A headlight that actually emits light could have a <DRM Positional Light> instance as the  source of illumination with a direction located at the light, directed out from the headlight.