The Physical Sky system in Maxwell Render uses a novel approach, offering a wide range of real-life and physically correct parameters to control the look of the sky and the subsequent lighting in the scene. Results range from common Earth values to exaggerated fantasy skies. Users can create pre-sets of sky settings to quickly load a new sky, or share their pre-sets with other users. It’s also possible to save the current sky as an HDR map.
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- From Disk: Allows you to choose a location to load a .sky pre-sets file.
- From Google Earth File: Allows you to choose a location by loading a Google Eath location file in .kml or .kmz formats.
- Preset: The dropdown will list all the saved pre-sets found in the Maxwell/ skies folder.
Save:
- As Preset: Saves a .sky preset file in the Maxwell/ skies folder.
- As HDR: First specify a location for the HDR file, then a resolution. The default format is a longitudinal HDR map (2:1 width to height ratio).
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• Turbidity Coefficient: Defines the concentration and amount of particles in the atmosphere. A value of 0 creates a perfectly clear sky (in which case the next three parameters won’t have any effect). 0.01 is a good value for low turbidity, e.g. a sky with very few aerosols in it so that it will appear almost clear. 0.04 is a good medium value and 0.1 is a high value. Raising the amount of particles in the atmosphere will usually result in a darker sky and darker scene illumination, but the effect depends also on the Scattering Asymmetry parameter (see below). In bright daylight situations and with a positive Scattering Asymmetry, raising the Turbidity Coefficient will at first desaturate and brighten the sky. Raising the parameter further will start to darken the sky. With negative asymmetry, the sky will begin to desaturate and darken. The following images show this effect:
Raising the Turbidity Coefficient in sunset situations will darken the sky. Remember that you can also raise the ISO of the camera in these cases, which can reveal an interesting sky.
Left: Default settings (0.04) Center: Turbidity 0.65, Scatt Asymmetry 0.7 Right: Turbidity 0.65, Scatt Asymmetry -0,7
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Note: Very high Turbidity Coefficient values such as 0.5 are also possible for very dense aerosol atmospheres, for example after a volcano eruption. |
• Wavelength Exponent: Defines the average size of the particles in the atmosphere. The particle size influences which wavelengths of light are absorbed and which are scattered. You can greatly vary the coloration of the sky by changing this parameter, and the effect of the Wavelength Exponent will be more visible the higher you set the Turbidity Coefficient. Having a lower value than the default 1.2 will have a desaturating effect on the sky. Higher values than the default will at first increase the saturation of the sky, until gradually turning towards green and then orange:
Left: Default settings (Wavelenght Exp 1.2) Center: Wavelenght Exp 10 Right: Wavelenght Exp 30
• Reflectance: Refers to the albedo of the aerosols, or the rate of energy scattered and absorbed by the aerosols. Higher values will scatter more light from the aerosols which will brighten the sky and scene illumination. Values range from 0 to 1. A value of 1 means that all light that interacts with the aerosols scatters, and none is attenuated.
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