Name

The shader’s name. Enter any name you like, or leave the default.

Zenith

The base color of the sky directly overhead

Horizon

The color of the sky at the horizon

Horizon/Zenith Bias

The bias between Horizon and Zenith color. A value greater than 0.5 results in the sky color being more inclined to the Zenith color than the Horizon color, and vice versa.

Y Rotation

The rotation of the sky around the center of the zenith

Cloud Color

The color of the clouds. Mars has red ones, we like white ones.

Cloud Limit

There are no clouds below this angle. The angle is measured positively from the horizon toward the zenith, in degrees. This parameter may be used to reduce any aliasing problems that may arise on the horizon.

Cloud Diffusion

Controls how much the clouds have diffused in the sky. A high value results in thin clouds; a low value gives the appearance of thick clouds. This parameter in conjunction with Cloud Limit can be used to simulate atmospheric haze.

Offset

Here, Width and Depth control the offset in the cloud texture in the X and Z directions, respectively. If the clouds are to move in a general direction (due to heavy winds in the troposphere, presumably), these are the values to animate.

Amplitude

Defines the cloud fractal’s amplitude. Note that this is only the amplitude of the first iteration, and successive iterations may raise the local amplitude further.

Ratio

The amplitude decay of the fractal iterations. It is defined as the ratio of the amplitudes of two successive iterations. For values less than 1, successive iterations will have decreasing amplitude; for values greater than 1, they increase in amplitude and the fractal becomes unbounded.

Iterations

Clouds are soft, so few iterations are necessary.

Turbulence

Creates a more turbulent-looking cloud fractal.

Animate

Makes the clouds animatable with the time parameter.

Animation Speed

Only activated once you check the Animate option. Defines the speed of the animation.

X, Y Scaling

The clouds are placed on the planet using a lollipop mapping. This means there will be stretching and a seam at the South pole (negative Y direction). Scaling is in kilometers for convenience, so that a scaling of 1 gives the clouds’ largest features 1-km diameter.

Rotation

Rotates the fractal; useful for eliminating visual artifacts due to repetitiveness in the fractal.

X, Y Translation

Offsets the cloud fractal. This can be animated to produce a wind effect.

Sky Mirror

Makes the ground a mirror image of the sky (ceiling).

RGB Intensity

Uses the intensity of the color in the texture file to determine the blend.

Alpha Channel

Uses the alpha channel of the texture file to determine the blend.

None

No blending. The texture dominates.

Real Ground

Causes the texture to do some additional calculations for the ground to allow it to be at a finite distance. In fact, the ground is placed at the Y position 0. This allows objects to change appearance as they move along the ground. Also, the effect of Ground Limit and Ground Diffuse change, and only the Ground Horizon color is used as a background color to the texture. Otherwise, both the sky and the ground are infinitely far away in all directions so that translations have no effect.

Base Color

Defines the color of the ground center, directly below you or the camera.

Horizon Color

Defines the color of the ground nearest to the horizon.

Horizon/Base Bias

The bias between the Base Color and the Horizon Color.

Limit

There is no texture displayed in the angular sector that this value defines. The angle is measured positively from the horizon toward the base, in degrees. When “Real Ground” is selected, however, this limit is not in degrees but in units of “distance.” This is a product of the distance to the point on the texture and how obliquely the ray strikes the texture. So, if the texture is either far away, or viewed at an oblique angle, or both, it is “distant.” In this case, try values of 500-1000 to start with.

Diffusion

Increasing this value blends the area outside the Ground Limit into the ground texture, producing a smooth transition between them. Essentially, the base ground color is allowed to exponentially diffuse into the texture. This gives the texture a hazy appearance as it approaches the horizon. When “Real Ground” is on, the effect is slightly different. Then this value specifies the number of units of “distance” over which the Ground Horizon color blends into the ground texture.

X, Y Scaling

Width and Depth determine the scaling of the Ground Texture in the X and Z directions, respectively. High values stretch the texture while lower ones make the texture repeat more often.

X, Y Rotation

Rotates the X and Y direction.

X, Y Translate

Here Width and Depth control the offset in the Ground Texture in the X and Z directions, respectively.