Category: mental ray > Environment
This shader provides the standard CIE sky model (both clear and overcast) that is used for lighting analysis. It is a colorless (grayscale) model, so it is intended for analysis purposes rather than generating visually pleasing images. It has the advantage of following a standardized (known) luminance distribution.
This shader shares many parameters with the mia_physicalsky shader and works in the same way. It is designed to be used together with the mia_physicalsky and mia_physicalsun shaders.
| Name |
The name of the shader node displayed in the render tree. Enter any name you like, or leave the default. |
| on |
Activates this shader. |
| rgb_unit_conversion |
Converts the output to something other than true photometric units. If this value is 1 1 1, both the values returned by the mental ray shader API functions mi_sample_light (for the sunlight) and mi_compute_avg_radiance (for the skylight), when sent through the mi_luminance function, will numerically match photometric values in lux. Since the intensity of the sun outside the atmosphere is calibrated to 127500 lux, this is very bright when seen compared to a more classic rendering, where light intensities generally range from 0 to 1. The RGB Unit Conversion parameter is applied as a multiplier and should be set to a value below 1 (such as 0.001 0.001 0.001) to convert the raw lux value to something more manageable. For convenience, the value of 0 0 0 is internally set so that 80000 lux (approximately the amount of light on a sunny day) equals the classic light level of 1. |
| auto_luminance |
The luminance of the sky can be defined by setting either the zenith_luminance parameter or a known diffuse_horizontal_illuminance value, but not both. |
| zenith_luminance |
Defines the luminance of the sky using a candela per square meter measurement. |
| diffuse_horizontal_illuminance |
Defines the luminance of the sky using a specific lux value. |
| overcast |
When overcast is zero, the CIE Clear Sky model is used. When overcast is 1.0, the CIE Overcast model is used. In-between values is a linear interpolation of the two models. |
| The following Sun parameters affect the visible result (what the camera sees and what is seen in reflections and refractions), but not the final gathering result. This is because this shader treats rays differently. Direct rays from the camera, as well as reflection and refraction rays, see the "entire" sky effect, including the Sun parameters. However, since the lighting already has a direct light that represents the sun (using the mia_physicalsun shader), the sun disk is not visible to the final gathering rays. |
|
| sun_direction |
The direction of the sun disk. |
| sun |
Pick a light (the sun) from the pop-up explorer. The light you choose becomes the controller for the direction of the shader. It should be the directional light that represents the sun, such as the same light that has the mia_physicalsun shader. This makes the visible sun disk automatically follow the direction of the actual sunlight. |
| y_is_up |
Defines what constitutes "up". In Softimage, the Y axis is up and this parameter should be on. |
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