Medium Volume

 

Volumetrics shading is done using the Medium Volume VOP node, linked to the Medium input of a MaterialThe representation of the surface or volume properties of an object. (Figure 1).

Medium_Volume_Fig01_Houdini_v2021.JPG

Figure 1: The Volume MediumA shading system designed to render volumes such as smoke and fog. node connected to a Specular materialUsed for transparent materials such as glass and water.

 

Volumes can have ScatteringDefines how fast light gets scattered when traveling through the medium., Emission and AbsorptionDefines how fast light is absorbed while passing through a medium.. These colors influence the volume's appearance. The Phase function also affects a volume as it would affect a Medium node, and modifying the Scale value of the volume scales the density values of the volume linearly. This will also potentially increase emission as absorption values are also used as particle density.

The Volume Step Length parameter's default value for the step length is 4 meters. If your volume is smaller than this, you will likely need to decrease the Step Length. Decreasing Step Length also reduces the render speed. Increasing this value causes the ray marching algorithm to take longer steps. Should the Step Length exceed the volume’s dimensions, then the ray marching algorithm takes a single step through the whole volume. To get the most accurate results, keep the Step Length as small as possible. For simplifying workflow, set the Volume Step Length to an acceptable value first.

Volumes are rendered in an unbiased way, and can scatter multiple times. They can also cause self-shadowing effects. To reduce the maximum scatter events in a volume, reduce the DiffuseAmount of diffusion, or the reflection of light photons at different angles from an uneven or granular surface. Used for dull, non-reflecting materials or mesh emitters. Depth in the Kernel node.

How to use the Volume medium is covered in more detail in the Effects Overview section.