RENDERMAN 22 DOCUMENTATION

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An environment light that uses a simple physical model for terrestrial daylight under clear or hazy skies. The sky model is based on A Practical Analytic Model for Daylight by A.J. Preetham, Peter Shirley, and Brian Smits. The solar disk model is adapted from H.C. Hottel's A Simple Model for Estimating the Transmittance of Direct Solar Radiation Through Clear Atmospheres, with parameters curve fitted for turbidity from physical data and a simple limb darkening model.

 

Parameters

Intensity

Scales the contribution of this light linearly.The light intensity is computed using physical units which are typically 100.000 times too intense for regular RGB rendering. We scale it internally by 1e-e5 to generate pleasing illumination levels.

Exposure

Specifies the exposure of the area light as a power of 2. Increasing the exposure by 1 will double the energy emitted by the light source. A value of 0 produces an intensity of 1 at the source, -1 produces 0.5.

 

Direction

The apparent direction towards the center of the sun. The zenith is at +Z (for noon light) and the horizon is in the XY plane (for sunrise/sunset). Note that the Z component must non-negative. Ignored if a month is given.In some DCC application, like Maya for example, you can manually alter the Sun direction using a manipulator in the viewport.

 

Haziness

The turbidity of the sky. The lower limit of the model is 1.7 for an exceptionally clear sky, and 10, for an inversion, is the upper limit.

 

Sky Tint

Tweak the sky's contribution and color. The default, white, gives results based on measured physical values.

 

Sun Tint

Tweak the sun's contribution and color. The default, white, gives results based on measured physical values.

 

Sun Size

Scale the apparent size of the sun in the sky. Leave at 1 for a realistic sun size with an 0.55 degree angular diameter.

 

Month

Month of the year, 1 through 12. The default, 0, means to use the explicitly given sun direction instead of automatically computing it.

 

Day

Day of the month, 1 through 31.

 

Year

Four digit year.

 

Hour

Hours since midnight, local standard time. May be fractional to include minutes and seconds. If daylight saving time is in effect, subtract 1 to correct to standard time.

 

Zone

Standard time zone offset from GMT/UTC in hours. Positive for east, negative for west. For example, this would be -8 for Pacific time.

 

Latitude

Latitude in degrees. Positive for north, negative for south. Ranges from -90 to +90 degrees.

 

Longitude

Longitude in degrees. Positive for east, negative for west. Ranges from -180 to 180 degrees.

 

 


Refine

 

Specular Amount

Amount of specular light that is emitted. This is a non-physical control.

 

Diffuse Amount

Amount of diffuse light that is emitted. This is a non-physical control.

 


Shadows

Note: All shadow parameters will be ignored if the light's bidirectional is enabled.

 

Enable Shadows

Enable raytraced shadows.

 

Shadow Color

The color of the shadows cast by emitted light. This is a non-physical control.

.0 0.0 0.0

Shadow Distance

The maximum distance of the shadow starting from the position of the point being shaded. -1.0 is unset which will use the distance between the point being shaded and the point on the light.

 

Shadow Falloff

The distance from the light at which shadow falloff begins. -1.0 turns off shadow falloff.

 

Shadow Falloff Gamma

The gamma of the shadow strength in the falloff zone.

 

Trace Subset

Set of geometry to consider for traced shadow intersection. If this is not specified, all geometry are considered for traced shadow intersection.

 

Don't Trace Subset

Set of geometry to ignore for traced shadow intersection. If this is not specified, no geometry is ignored for traced shadow intersection.

 

 


Advanced

 

Trace Light Paths

Enable light and photon tracing from this light.

 

Thin Shadow

Enable thin shadow (fake colored shadows for transparent objects) and disable refraction caustics for this light. This parameter will be ignored if Trace Light Paths is enabled.

 

Light Samples

Specifies an override of the number of light samples to be taken for this light source. If set to something other than zero, it will override the sampling performed by the integrator. You might find need for this if you have unsolvable noise from this light and need mroe samples.

 

Light Group

Specify the light group name used for light group LPEs. This is useful to generate per-light AOVs for later adjustment in compositing.

 

 


Presets

RenderMan for Maya includes useful presets for specific times of day.