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Parameters and tooltips of Volumetrics beta0.9

Volumetrics/root:

Preview quality(%)
How precise (approximately) RTR should work. Also have effect on automatic adjustments. Recommended values: 10..50
Vol. Shadows
Volumetric shadows. Both isosurfaces and clouds can cast this type of shadows.
Traced shadows
Raytraced shadows; Only Surfaces can cast this type of shadows.
Ambient
Uniform ambient light. I recommend to use light from above, side and below instead. Currently applied only to surfaces(reason: in reality, ambient lighting of clouds is different from landscape's).
Light from above
Ambient light coming from above. Currently applied only to surfaces. To use it on MojoWorld terrain and MojoWorld objects, put 'Vol. ambient for MojoWorld' node (Volumetrics category) into MojoWorld's Ambient Light
Light from side
Ambient light coming from sides. Currently applied only to surfaces. To use it on MojoWorld terrain and MojoWorld objects, put 'Vol. ambient for MojoWorld' node (Volumetrics category) into MojoWorld's Ambient Light
Light from below
Ambient light coming from below. Currently applied only to surfaces. To use it on MojoWorld terrain and MojoWorld objects, put 'Vol. ambient for MojoWorld' node (Volumetrics category) into MojoWorld's Ambient Light
Diffuse sunlight
Ambient light coming from sunlight direction. Currently applied only to surfaces. To use it on MojoWorld terrain and MojoWorld objects, put 'Vol. ambient for MojoWorld' node (Volumetrics category) into MojoWorld's Ambient Light
Opposite sunlight
Ambient light coming from direction opposite to sunlight. Currently applied only to surfaces. To use it on MojoWorld terrain and MojoWorld objects, put 'Vol. ambient for MojoWorld' node (Volumetrics category) into MojoWorld's Ambient Light
Detail
How much detailed fractals must be. Default is good enough; if you get something looking smoother than it should, increase this parameter. Values smaller than 1 is not recommended unless you know what you are doing - it may make your terrain to morph noticeably when rendering resolution is changed and/or camera is moved
Lowest detail distance
At what distance details stop decreasing. Smaller values is slower. Default is good enough, practically no need to change
Max. steps
Currently unused.
Exposure
Works similarly to real photo camera. Bigger values make image brighter, smaller make darker. You can make stars have proper brightness and increase this parameter to make nightside renders
Photofilm
Simulation of photofilm. Usually makes render look more realistic, but somewhat desaturated. Prevents 'over-burning' of render if brightness is too big. It is recommended to turn this on as it helps preserve image for postwork even if render was under/over exposed (bit like HDRI)
Gamma
Gamma correction. If you feel like, try experimenting with this parameter. Though, it could be better to do gamma correction in postwork
Color error
Precision of coloring. Default is good enough, not much need to change. Smaller values is slower, but normally don't give noticeable difference in render quality
Vol. lighting radius
If 'Lighting transform method' is set to 'none', defines up to how many meters away from camera shadows will work. If 'Lighting transform method' is set to 'method1', does nothing
Vol. lighting resolution
Resolution of lighting. For previews, use 500, for final, use ~2000 . Bigger values is better but is also slower and use more RAM
Lighting transform method
Better set it to method1 unless you're doing animation where camera moves much. It's some internal thing, no explanations(sorry). Maybe I should have blocked it in this release
Lighting top precision(m)
What maximal precision shadows will have. Smaller values give better quality but are slower and use more RAM. Specified in meters, currently has effect only if 'Lighting transform method' is set to method1.
Lighting error bound
Maximal lighting error. Smaller values give better quality, but use more RAM.
Max. ray bounces
Raytracing: max. number of ray bounces. You may need bigger values for scenes with lot of multiple reflections
Hide mjw. planet
If checked, MojoWorld planet will not be rendered.
Receive shadows from Mojo
If checked, Volumetrics will receive shadows from MojoWorld. That is, shadows cast by MojoWorld objects will be visible ON Isosurfacesand ON Clouds. offtopic: For making shadows cast by Isosurfaces and Clouds be visible ON MojoWorld terrain, open Sunlight Editor, and in Sunlight Color, make function graph with single node 'Vol. shadows ...' (Volumetrics category).You can get more detailed explanation on website.

Surface

Active
If unchecked, this thing will not be rendered.
Cast vol. shadows
If unchecked, this thing will not cast volumetric shadows.
Cast trac. shadows
If unchecked, this thing will not cast raytraced shadows.
Lowest altitude
Isosurface is contained between lowest altitude and highest altitude. Also have effect on UVposition in functions(UVposition.x is 0 at lowest and 1 at highest; you can use it instead of altitude)
Highest altitude
Isosurface is contained between lowest altitude and highest altitude.
Shape
Put there texture that controls shape of isosurface. In places where value is below 0 , you'll have solid, where above, you'll have clean air. It's somewhat like effect of temperature on water and ice (where <0 you get ice)
Min step size
Minimal step size. Default should be good enough
Refinement steps
How many refinement steps to do. Default should be good enough
Precision
Precision of intersection solver. Default should be good enough
Adaptive
Automatic adjustments. Works only if RTR preview is turned on.
Reliability
Increase this if you have artifacts. Controls how automatic adjustment works. Have effect on rendertimes (bigger usually slower, but not always).
Step scale
This parameter is changed automatically if Adaptive is checked and RTR is on.
NanoDetails
Experimental parameter. If checked, isosurface will do lighting with submillimeter precision. Slows things down

Shader

Diffuse
Color of diffuse component
Shininess
How shiny you want specular highlight be (bigger values make it more shiny, i.e. smaller spot size)
Specular
Color of specular highlight
Glow
Glow color
Reflection
Check it if you want reflections
Refraction
Check it if you want refractions (doesn't work in this version)
Fresnel specular
When checked, like in real world, brightness of specular highlight will depend to angle of incoming light and to index of refraction of material (in other words, when it is checked, specular highlights looks less CG-like and can be more realistic)
IOR
Index of refraction. Like real world, it has effect on two things: a.) how much light refracts (something that you probably knew already :-), b.) what portion of light goes through and what portion of light reflects off boundary. (somewhat less widely known effect) Some sample values: air or vacuum = 1 , water = 1.33 , ice=1.309 , glass = 1.5 to 1.9 , diamond = 2.42 . To simulate metals, use large values, like 200, so the reflection will be metal-like
Reflect color
Color of reflection (for most kinds of materials (e.g. water, glass, polished rock, etc.) use white)
Refract color
Color of refraction (for most kinds of materials (e.g. water, glass, polished rock, etc.) use white)
Active
If unchecked, this thing will not be rendered.
Lower altitude
Atmosphere is contained between lowest altitude and highest altitude. These parameters also have effect on UVposition in function graphs (UVposition.x is 0 at lowest and 1 at highest; you can use it instead of altitude) so height of cloud layer can be specified with only lowest and highest alt.
Higher altitude
Atmosphere is contained between lowest altitude and highest altitude.
Density
Controls density of the clouds. Internally, density is clamped to 0..1 range. To control overall density, use 'Visibility distance' instead
Extinction
Defines what color of light is trapped(scattered or absorbed) the most. For example, if extinction is greenish blue, after light passes through much atmosphere you will get red because green and blue was either scattered or absorbed Reemission(parameter right below) defines how much of this light is scattered (rest is absorbed). i.e. If extinction is blue and reemission is white, it blue light is scattered the most. If reemission is black, blue light is absorbed the most
Reemission
Defines what part of trapped light is scattered (rest is absorbed). You can think of it as color of dust particles. See tooltip for extinction.
Emission
Somewhat like glow; defines how much light is produced by cloud. Can also be used for ambient lighting.
Shadow darkness
Defines how much effect absorbing and scattering have on lighting (shadowing). Example: 0 = no effect on lighting (no shadows), 0.5 = half effect, 1 = full effect
Anisotropic
Anisotropic scattering. Rayleigh simulates scattering by molecules(e.g. scattering by very clean air), others simulate scattering by fog/dust particles.
Visibility distance(m)
Sort of visibility distance, specified in meters. Smaller values make denser atmosphere.
Min step size
Minimal step size. Have effect on render times. Good starting value: 1/15 of 'Free path length' (parameter right above this one).
Adaptive
Automatic adjustments. Works only if RTR preview is turned on.
Reliability
Increase this if you have artifacts. Controls how automatic adjustment works. Have effect on rendertimes (bigger usually slower, but not always).
Step scale
This parameter is changed automatically if Adaptive is checked.
Fixed steps
Obsolete.
Jitter
Jittering amount. Use values between 0 and 1, recommended value:0.7 for air atmospheres, 0.3 for clouds. Have effect on image quality, sorta 'color bands versus noise'.