mental ray Architectural and Design Visualization Shader Library

68 3 Sun and Skygo below a certain angle. This parameter tweaks this angle. The total range availablerange is somewhat extreme, reaching from -10.0 (the horizon is “straight down”) to 10.0(the horizon is at the zenith)! In practice, only much smaller values are actually useful,like for example -0.2 to push the horizon down just below the edge of a finite visibleground plane.Note: The horizon height affects not only the visual representation of the horizon inthe mia physicalsky shader, but also the color of the mia physicalsun itself, i.e. the pointwhere the sun “sets” will indeed change for a nonzero horizon height.• horizon blur sets the “blurriness” with which the horizon is rendered. At 0.0 thehorizon is completely sharp. Generally low values (lower than 0.5) are used, but the fullrange is up to 10.0 for a horizon which only consists of blur and no actual horizon at all.horizon height=0.0, horizon blur=0.0horizon height=-0.3, horizon blur=0.2• ground color is the color of the virtual ground plane. Note that this is a diffusereflectance value (i.e. albedo). The ground will appear as if it was a Lambertian reflectorwith this diffuse color, lit by the sun and sky only, does not receive any shadows.Red groundGreen groundNote in the above images how bounce-light from the ground tints the walls of the house.Also note that the virtual ground plane does not receive shadows.Many sky models neglect the influence from bounce light from the ground, assumingonly the sky is illuminating the scene. To compare the output if the mia physicalskywith e.g. the IES sky model one must therefore set the ground color to black.• night color is the minimum color of the sky - the sky will never become darker thanthis value. It can be useful for adding things like moon, stars, high altitude cirrus cloudsthat are lit long after sunset etc. As the sun sets and the sky darkens, the contributionfrom night color is unaffected and remains as the “base light level”.