Webots Reference Manual - chapter 3 - section 46

Webots Reference Manual


3.46 SpotLight

Derived from Light.

SpotLight { 
  SFFloat ambientIntensity  0        # [0,1]
  SFVec3f attenuation       1 0 0    # [0,inf)
  SFFloat beamWidth         1.570796 # [0,pi/2)
  SFColor color             1 1 1    # [0,1]
  SFFloat cutOffAngle       0.785398 # [0,pi/2)
  SFVec3f direction         0 0 -1   # (-inf,inf)
  SFFloat intensity         1        # [0,1]
  SFVec3f location          0 0 10   # (-inf,inf)
  SFBool  on                TRUE
  SFFloat radius            100      # [0,inf)
  SFBool  castShadows       FALSE
}

3.46.1 Description

The SpotLight node defines a light source that emits light from a specific point along a specific direction vector and constrained within a solid angle. Spotlights may illuminate Geometry nodes that respond to light sources and intersect the solid angle. Spotlights are specified in their local coordinate system and are affected by parent transformations.

The location field specifies a translation offset of the center point of the light source from the light's local coordinate system origin. This point is the apex of the solid angle which bounds light emission from the given light source. The direction field specifies the direction vector of the light's central axis defined in its own local coordinate system. The on field specifies whether the light source emits light--if TRUE, then the light source is emitting light and may illuminate geometry in the scene, if FALSE it does not emit light and does not illuminate any geometry. The radius field specifies the radial extent of the solid angle and the maximum distance from location that may be illuminated by the light source - the light source does not emit light outside this radius. The radius must be >= 0.0.

The cutOffAngle field specifies the outer bound of the solid angle. The light source does not emit light outside of this solid angle. The beamWidth field specifies an inner solid angle in which the light source emits light at uniform full intensity. The light source's emission intensity drops off from the inner solid angle (beamWidth) to the outer solid angle (cutOffAngle). The drop off function from the inner angle to the outer angle is a cosine raised to a power function:


    intensity(angle) = intensity * (cosine(angle) ** exponent)

    where exponent = 0.5*log(0.5)/log(cos(beamWidth)),
          intensity is the SpotLight's field value,
          intensity(angle) is the light intensity at an arbitrary
              angle from the direction vector,
          and angle ranges from 0.0 at central axis to cutOffAngle.
  

If beamWidth > cutOffAngle, then beamWidth is assumed to be equal to cutOffAngle and the light source emits full intensity within the entire solid angle defined by cutOffAngle. Both beamWidth and cutOffAngle must be greater than 0.0 and less than or equal to π/2. See figure below for an illustration of the SpotLight's field semantics (note: this example uses the default attenuation).

The light's illumination falls off with distance as specified by three attenuation coefficients. The attenuation factor is 1/(attenuation[0]+attenuation[1]*r+attenuation[2]*r2), where r is the distance of 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 must be >= 0.0.

spot_light

Figure 3.30: Spot light

release 7.0.2
Copyright © 2012 Cyberbotics Ltd. All right reserved.