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mental ray Sun & Sky 1317
param eters are all guided by the mr Sk y light,
which is the central point of control.
With parameter inheritance, you can concentrate
on tweaking the parameters in one spot (mr Sky)
and, as long as Inherit From mr Sky is on for both
mr Sun and mr Physical Sky, you’re sure to obtain
consistent results.
Int er f a ce (common pa ra meter s)
The most important common parameters are
those that drive the entire shading and colorization
model.
Note: mr Sun and mr Physical Sky can inherit
parameters f rom mr Sky even if the latter is off.
Haze—Theamountofwatervapororother
particulatematterintheair. Possiblevalues
range fro m 0.0 (a completely clear day) to 15.0
(extremely overcast, or a sandstorm in the Sahara).
The Haze value influences the intensity and color
of the sky and horizon, the intensity and color
of sunli ght, the softness of the su n’s shadows,
the softness of the glow around the sun, and the
strength of the aerial perspec tive.
Hor izon Height—The vert ical position of the
horizon.
The default value, 0.0, places the horizon at a
standard height. However, because the horizon is
infinitely far away, this can cause trouble joining
upwithanyfinitegeometrythatissupposedto
representtheground. Itcanalsocauseissues
rendering locations that are supposed to be at a
high altitude, like mountain tops or t he top of New
York skyscrapers w here the horizon really is visibly
“below” the viewer.
Thisparameterallowstuningthepositionofthe
horizon. Note that this horizon doesn’t act ually
exist at a specific height in 3D space; it is a shading
effect for rays that go below a certain angle. This
parameter tweaks that angle. The total range
available range 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. For
example, to push the horizon down just below the
edge of a finite visible ground plane, use –0.2.
Note: The Horizon height affects not only the visual
representation of the horizon in the mr Sky light,
but also the color of the mr Sun itself. In other
word s, the point where the sun “sets” wil l change
for a Horizon height settings other than 0.0.
Hor izon B lur —The “blurriness” with which the
horizon is rendered.
At 0.0 t he horizon is completely sharp. Generally
only values lower than 0.5 are useful, but the full
range is up to 10.0 for a horizon that consists of
blur only, with no actual horizon at all.
Ground Color —The color of the virtual ground
plane. Note that this is a diffuse reflectance
value (that is, albedo). The ground appears as a
Lambertian reflector with this diffuse color, lit by