Houdini 20.0 Nodes Geometry nodes

Volume Ambient Occlusion geometry node

A node that generates the ambient occlusion field of the provided density field.

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Since 20.0


The Volume Ambient Occlusion SOP computes the ambient occlusion of the provided density field. It stores in a scalar field named occlusion how much each voxel sees its environment where 0 means there is no occlusion and 1 means fully occluded.

This node was initially created to accelerate cloud rendering where multiple scattering can be approximated by remapping the occlusion field at render time from dark values (for the cloud edges) to bright values (for the cloud interior). Although not physically accurate, this approach strikes a good balance between efficiency and visual quality.

For more information, see Cloud rendering with volume ambient occlusion.

Before and after using baked ambient occlusion.



A volume or VDB density field to generate the occlusion field.



Input density field with generated occlusion field.


Source Group

A primitive group identifying the density field to use.


The name of the generated field containing the ambient occlusion information.

Resolution Ratio

Defines the occlusion field resolution as a ratio of the provided density field. A value of 0.5 will yield an occlusion field of half the resolution of the provided density field. Smaller values are more efficient but less accurate.

Expand Voxels

Expand the active area of the occlusion field by the specified number of voxels. This is useful at render time to prevent the renderer from sampling outside the computed area during interpolation.


This parameter is only considered when VDBs are used. Volumes are densely computed and, therefore, not affected by this.

Volume Marching

Density Scale

A multiplier of the density field used for ambient occlusion computation only, leaving the original density field untouched. A value of 0.1 will make the density appear ten times more transparent to the ambient occlusion computation.

Transmission Cutoff

The level of transmittance where we consider the ray fully occluded and stop marching the density field. A value of 0.005 means that occlusion of 0.995 is considered fully occluded. Larger values are more efficient but less accurate.

Geometry nodes