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.

For information on working with Maya's volumetric fluids, click 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. Type: OpenVDB.


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'.

Filename

The location of the VDB file. 

Ensure that the IPR is not running when updating the file, otherwise, the bounding box will not display at the correct size in the viewport.

Grids

A 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.

Use File Sequence

Reads a sequence of VDB files.

Frame

Specifies the frame of the sequence to be rendered.

Keframe set for 'Frame' and hashtag used in 'Filename' when using VDB sequence

Automatic Step Size

Sets the minimum voxel size defined in the VDB as the step size.

Step Size

More information about volume Step Size can be found here.

Step Scale

Volume Padding

Compress

Velocity Grids

Velocity Scale

Velocity FPS

Motion Start

Motion End

Velocity Threshold

If you need to further edit the result of the reading of a channel, for instance, to color correct it, there are the Volume Sample RGB and Volume Sample Float shaders.

Type

Implicit

Volume implicit nodes can be used to load OpenVDB files for rendering volumes and implicit surfaces respectively.

Implicit type volume .vdb file

Solver

Threshold

Samples

Field Channel

Field

Reducing Noise

To reduce the amount of noise in a volume, you must ensure that any lights in your scene have sufficient volume samples, or alternatively that you have enough Camera (AA) samples.



Volumes and Atmosphere Volume

Currently, atmosphere_volume does not compose well against volumes. This is because atmospheres return a single flat result that is opacity mapped on top of whatever is in the background of the pixel.

Left: floor plane geometry hidden. Right: floor plane geometry visible. Fluid renders incorrectly.