Bake Volume surface node

Computes lighting values within volume primitives

All Parameters Example files

Given a point light, this operator computes lighting values for all input volume primitives and outputs them as volume triples representing Red, Green and Blue values.

The light transfer properties of the volumes can be modified to change their appearance when lit.

Parameters

Group

The primitive group to compute lighting values for.

Lightfield Name

The generated lightfield volumes will use this name as a prefix to .x, .y, and .z for their own names. This allows the light field to override shading attributes in Mantra.

Light Position

The position in world space of the light used to compute the volume lighting values.

Radiance

The intensity of the light being used to compute volume lighting values.

Absorption Coefficient

Determines how much of the light’s radiance is absorbed by the volume per unit density.

Scattering Coefficient

Determines the amount of light that is scattered (redirected) per unit density of the volume.

Emission Coefficient

Determines the amount of light per unit density that is released by the volume when struck by a light ray.

Isotropic Ratio

The proportion of light that is assumed to be isotropically scattered (redirected in all directions evenly) whenever scattering occurs within the volume.

Step Size

The step size is used when simulating the behavior of light rays within the volume. A smaller step size will produce better results, but take longer to compute.

Note

Using a step size larger than the voxel diameter of the volume being baked is not recommended due to lack of accuracy.

Density Scale

Scales the density of the volume being baked.

Do Multiple Scattering

Whether or not multiple scattering effects will be calculated.

Number of Rays

The number of light rays used to simulate multiple scattering effects. Using more rays can improve the appearance of rendered volumes, but at the cost of longer computation times.

K

Coefficient defining the directional tendencies of scattering within the volume. K ranges from -1, indicating perfect backward scattering, to 1, which is perfect forward scattering. A value of 0 will cause unbiased, fully random scattering.

Do Separate Color Passes

Whether to perform a different scattering simulation for each of the colors Red, Green and Blue.

When enabled, it is often necessary to increase the Number of Rays to eliminate a blotchy appearance of colors.

Optimize Light Transfer

When enabled, the operation will use previously computed light values wherever possible in order to reduce computation times.

The results of an optimized pass will not be as accurate as those of a non-optimized one.

Optimized Ray Depth

How deeply into the volume an optimized pass will cast its light rays before using previously computed values.

Lower values result in faster, less accurate calculations, while higher values cause longer computation times with more accurate results.

Note

Values less than 2 are not recommended, because the validity of previously computed values cannot be guaranteed with rays that short.

Conversely, values greater than the voxel resolution of the volume being baked have no advantage over a non-optimized pass. The Optimize Light Transfer option should be disabled instead.

Example files

bakevolume

$HFS/houdini/help/examples/nodes/sop/bakevolume/bakevolume.otl

Load | Launch

This example shows how to setup the Bake Volume SOP to compute the lightfield created by the shadowing of a fog volume. It then exports the fields properly to be rendered in Mantra by a constant volume shader.

Usages in other examples

Example name Example for