thinkingParticles fully supports saving volume data in OpenVDB file format. It is important to note that while OpenVDB is an open standard, there is no guideline or actual rule how such files store data. Scale or translation information in general are not defined and can vary largely by application. While 3ds Max uses a Z-Up axis system other applications may use a different reference axis system. OpenVDB files in general use their reference  coordinate system as Y-Up. To get more information about OpenVDB check the official  OpenVDB web page.

Also check out the short summary of OpenVDB in thinkingParticles.

ON - determines whether the operator is considered 'on' or 'off'. You can connect other operators to this input channel such as a Bool Helper to activate/deactivate the whole operator.

Time -  defines the local time for the operator when the user wants to override the default system time.

Writing - outputs either True or False, depending on the status of this operator. When writing a file this output is set to True else it will be set to False. This output is most relevant when writing out file sequences.

OpenVDB - lets you specify the OpenVDB “container” or satellite node. This workflow is similar to the Flow or Bullet physics solver mechanism. To learn more about it check out the OpenVDB satellite node.

PGroup - choose the particle Group to write its volume data to a file. Keep in mind, every particle found in this Group with a VDB volume attached will be written out as an individual file.

Include Sub Groups - when checked sub-groups of the selected main group are also used to look for particles with volume data attached to them.

Save To - click the Select Save File to bring up a standard windows file explorer Save dialog.

Grids To Save - check any volume Grids available to be saved into a VDB file.

Export Method - there are multiple export methods available.

1. Without Particle TM
2. Include Particle TM
3. All Particles in One

Add Particle Velocity To - particles with volume Grid data attached can transfer their  velocity information to the volume Grid. This might be useful to create a motion blur effect at render time based on the particle movement.

Float As Half - check this option to reduce the amount of memory used when creating a VDB file. However, this comes with a price of reduced numerical resolution/accuracy of the data in a volume Grid.

Include Particle TM - when checked, thinkingParticles will include the full transformation matrix so that when loaded back into tP or any other application in3ds max the position and size of the volume stays the same.

Mode - VDB files can be saved as single files or as a file sequences. The following modes are available:

1. Single Viewport Grab
2. Active Time Segment
3. Range

From, To - when Range is selected those settings become active. Set a start and end range to save VDB data to a file.

Sub Samples - defines the amount of sub samples to save  VDB files. A value of 0 means full Frame, a value of 1 is half Frame. Keep in mind, setting this to 1 for example means that 60 files will be created per second and so on. Other applications may not support this and may playback the animation much slower. Make sure the amount of sub samples matches your target application's possibilities.

Record In - when saving a VDB file sequence two rendering modes can be selected. This sets any render view dependent modifiers into their relevant output mode. Turbosmooth for example, is such a modifier it has the option for offering two mesh resolutions; one viewport mesh and one for the renderer.

1. Viewport Mode
2. Render Mode

Redraw Views - when checked the 3ds Max view ports redraw while saving a VDB file sequence.

Export - click this button to start the Export process.