Volume file formats, such as OpenVDB, will allow storage of much larger datasets while being optimized for random access to volume data, which is more efficient for rendering. OpenVDB is an open source C++ library comprising a novel hierarchical data structure and a suite of tools for the efficient storage and manipulation of sparse volumetric data discretized on three-dimensional grids.
Tutorials about working with volumes can be found here.
A tutorial on how to write volumes to OpenVDB from Houdini can be found here.
Volumes can only receive indirect lighting from other emissive volumes when the Volume Ray Depth is above 0.
Arnold Volume (VDB).
Custom AOVs are not currently supported with volumes.
To reduce the amount of noise in a volume, you must ensure that the lights in your scene have enough 'volume samples'.
The location of the volume VDB file.
Volume shader that is assigned to the volume. Typically this is a Standard Volume shader.
A space-separated list of OpenVDB grids to read and make available as channels in the volume shading context. Examples of Grid names are density, fuel, heat, temperature or velocity.
Either one vector grid (e.g., v or vel) or three float grids (e.g., vel.x, vel.y, vel.z) representing the velocity field, to be used for motion blur. No motion blur will occur if an invalid combination of grids or if no grids are specified. Note that all velocity grids declared here are also available as channels in the shading context.
Choose a step size relative to the voxel size.
Choose a step size (where an actual step size is given).
More information about volume Step Size can be found here.
Enable reading a sequence of VDB files.
The start frame of the VDB file sequence.
For example, if your sequence on disk goes from name1001.vdb to name 1100.vdb, you can pick the files from 1050 to 1080 by entering these values as the Sequence Start and the Sequence End respectively.
The timeline's frame at which the VDB sequence ends to be used.
If there are not enough files in the sequence to cover the Animation Start-End range, the sequence can be repeated, either from its start or in ping-pong mode.
Sets the playback speed of the volume's animation.
Create the Volume by going to Arnold in the Create Tab and select Volume. Click and drag in the viewport to create the volume.
Select from the VDB Grids that the volume has been saved with. A default Standard Volume shader will be assigned to it.
To reduce the amount of noise in a volume, you must ensure that any lights in your scene have sufficient volume samples, or that you have enough AA samples.
Smoke volume by Mads Droschler