Arnold OpenVDB Surface


OpenVDB dragon levelset available here

 

Volume file formats, such as OpenVDB, will allow storage of much larger datasets while being optimized for random access to volume and level set 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 the sparse volumetric, point, and level set data discretized on three-dimensional grids.

OpenVDB

The default implicit plugin is OpenVDB. In addition to the ray extents acceleration, auto bounding box and auto step size of the new volume API, it brings several production features such as velocity motion blur, scaling of velocity and step size and much more.

Grids

The grids to read from the OpenVDB data and provide as volume channels to shaders. You should specify at least one grid to read in. Note that KtoA will attempt to retrieve the bounding box of the volumetric data and display it in the viewer.

Solver

The solver to use to find ray intersections. Generally, this should be left on levelset, which is much faster with an actual level set data such as provided by OpenVDB.  uniform will also work, but is slower and requires a higher samples setting.

Field Channel

The grid data that provides the level set / signed distance field data. This is required to be set.

Threshold

The field value that is considered to be where the surface exists. Usually, this is zero, but making it slightly higher or lower can suck the surface in or out.

Samples

This governs how many taps on the field channel are allowed while trying to find the surface. For level sets, generally 2 is good enough, but sometimes more may be required for very complex level sets.

Auto Step Size

Auto step size, when turned on, will ignore the step size that is manually set. Instead, you can modify the step size from its natural value with step scale instead.  When turned off, you can manually set the step size.

Step Size

A scaling factor applied to the step size, mostly useful when the Volume Step is set to Automatic, to modulate the automatic value. For low frequency, smoke-like volumes, a value of 4 is a reasonable starting point.

Step size governs the minimum distance the solver will advance when trying to find the surface. If it is too low, the true surface may not be found; if it is too large, the surface may not be found accurately.  It is usually recommended to turn on auto step size rather than manually set this.

Step Scale

A scaling factor applied to the step size, mostly useful when the Volume Step is set to Automatic, to modulate the automatic value. For low frequency, smoke-like volumes, a value of 4 is a reasonable starting point.

Compress

Compress grids to reduce memory usage, enabled by default. This is a lossy compression, however in most cases renders will be almost the same. If there is a problem, however, this parameter can be used to disable lossy compression.For large grids, this can be very helpful, although it does carry a small premium in render time.

Velocity Grids

Either 1 vector grid (eg. v or vel) or 3 float grids (eg. vel.xvel.yvel.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.

Velocity Scale

A scale factor for the velocity field. A value of 0 disables motion blur.

Velocity FPS

Sets the frames per second velocity value.

Motion Start

Specifies the shutter open value at the current frame.

Motion End

Specifies the shutter close value at the current frame.

Transform

Set the transform (which can be interactively modified in the viewer with manipulators) for the surface.

 

 

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