This page provides information on the Output rollout for a LiquidSim object.


The Output rollout holds the controls for the cache file export.

UI Path: ||Select Liquid Simulator | LiquidSim object|| > Modify panel > Output rollout






Simulation Cache Save Path | simoutput – This is the directory and the name template for the output cache files. It uses the $(scene_path) macro by default, and there are also other available macros as listed below. To set up rendering and simulation cache paths manually, see How to change the default Phoenix paths on the Tips and Tricks page.

Click Here to expand additional $(VARIABLE) information

$(scene_path) – $(dir)\$(scene)_Phoenix_frames\$(nodename)_####.aur
$(scene_dir) – $(dir)\$(scene)_Phoenix2_frames\ND$(handle)_$(nodename)_####.aur
$(implicit) – Same as $(scene_dir)
$(dir) – The scene directory.
$(scene) – The scene file name.
$(handle) – A unique number of the node.
$(nodename) – The name of the node.
$env(<variable_name>) – An environment variable. See Using Environment Variables below.

#### is the frame number formatted with at least as many digits as the hash signs. If the frame digits are less than the hashes, the number is padded with zeroes to the left. For example:


Frame Number#######

Since version 3.00.02, Phoenix FD can export VDB grid data. Check the How to export Phoenix FD simulation to OpenVDB format video.
Appending a .vdb extension after the Output Path tells Phoenix to write its data in the OpenVDB format.

Particle data can also be exported using the .aur or the .vdb format. Phoenix can convert particles from already simulated Phoenix FD .aur caches into the .prt format as a post-process using the PhoenixFD Export PRT Particles dialog or to .vdb format using the Cache Converter tool.

 Clicking the "..." button will open a menu with the following options:


Browse - Opens a dialog for choosing one of several cache file types. Phoenix FD can import *.f3d and *.vdb files from other fluid simulator software products. Supported file types are Phoenix FD *.aur, Field3D *.f3d and OpenVDB *.vdb.  See How to import and render simulations from FumeFX, Houdini and Maya for more information.  

Delete Cache Files - Clears the cache files matching the provided Simulation Save Path pattern.

Reset to Default - Resets the Simulation Save Path to the default value of $(scene_path).

Show File Name - Evaluates the full disk path provided to the Simulation Cache Save Path parameter.

Help - Opens the Help page for the Output tab of the Phoenix FD Liquid Simulator.

Storage quality | storage_quality – The output grid and particle channels are compressed by default in order to increase the performance (faster cache loading) and to avoid excessive memory consumption. This parameter can range from 8 to 20 - 8 is the smallest size, while 20 is the best quality and is uncompressed. If this value is set too low, different artifacts may start appearing depending on the type of scene. For grid channels, artifacts shaped like horizontal slices may appear in preview and rendering. For particle systems such as Liquid or Foam, the artifacts would look like ordered lines of particles, as in the following comparison (click to zoom in):

Backup interval | backup – The frame interval between backups of the full simulation state. A stopped simulation can be restarted from such frames (see the Restore option in the Simulation rollout). To make restoring possible from every frame, set this value to 1. A value of 0 means no backup frames will be exported. 

Compress particles | prtcompress – Enables compression of particle systems, which optimizes system performance when the simulation involves a high particle count (50M or more). In such cases, the cache files can reach up to 1GB each unless the particle system is compressed.


Example: FLIP/Liquid compression artifacts

For particle systems such as Liquid or Foam, the artifacts would look like ordered lines of particles, as in the following comparison (click to zoom in):

Storage quality = 19


Storage quality = 14
(artifacts in the lower left corner)


Storage quality = 8


Output Particles

The particle export parameters share a user interface to keep the user interface compact. Each particle system can be selected individually from the drop-down list, and the output settings can be selected for that particle system. When a particle system is selected again, the same settings are retained.



Velocity – The particle velocity channel will be exported. Use this option when you need motion blur for the particle systems such as Foam, Splash, etc.

ID – The ID channel will be exported. This channel is used during rendering to identify each particle. Use it when render time size variation is needed, or when frame blending will be involved (animated frame index or non-integer play speed).

Age – The particle age channel will be exported. This channel is appropriate only for particles with animated particle ages such as those included in the Phoenix Particle Texture, PHXSource helper, and PHXFoam shader. In this case, the parameter will be animated not using the absolute global time, but the particles' age.

 The Age channel is affected by the Time Scale option under the Dynamics roll-out which acts a multiplier for the Age.

RGB – The particle RGB channel will be exported. You can use this for simulations where you are mixing different particle colors or you shade the particles by the particle RGB channel through a PhoenixFDParticleTex. Also, enable this if you want to be able to preview the RGB channel as a particle color in the Viewport.

Size – You would need this channel to be exported if you would like to use the simulated particle sizes when rendering. Note that the WetMap particle system does not export the Age channel and its Size channel decreases with time.

Viscosity - The particle Viscosity channel will be exported. Enable this if your Resimulation requires the calculation of viscosity.

Texture UVW – The particle Texture UVW channel is exported. Enable this to generate texture mapping coordinates that follow the movement of the fluid. 

All the info from this section is kept in text form in a single text parameter, which is accessible through MAXScript under the name prt_expmask

Grid channels

This section determines which channels are exported to cache files in the form of a voxel grid. Currently, only the liquid particles can be automatically converted to a grid during export, while all the other systems (e.g. Foam, Splash, etc.) are exported only as particles.



Liquid | keep_t – Export the liquid amount. This is needed so that you can mesh the liquid channel.

RGB | keep_rgb – Export the RGB color. You can use this for simulations where you are mixing different liquid colors or materials through a Phoenix FD Grid Texture.

Velocity | keep _vxyz – Export the velocity. This is needed for motion blur of the liquid mesh.

Viscosity | keep_visc - Export the Viscosity channel. Required for variable Viscosity simulations  You may also choose to enable this if, for instance, your setup requires that you use the Viscosity channel as a mask through a Phoenix FD Grid Texture.

Texture UVWkeep_texuvw – Export the Texture UVW channel. Enable this to generate texture mapping coordinates that follow the movement of the fluid. 

Special | zmr – Export internal or special channels into the Special channel (alias to the Smoke channel) so they can be visualized using one of the volumetric shaders of the FireSmoke Simulator (with Mode set to VolumetricVolumetric Geometry, or Volumetric Heat Haze). Such channels can also be read by the Grid Texture and used for rendering.

Solid Voxels – Exports the solid voxels as smoke. Voxels covered by many obstacles contain more smoke.
Divergence Symm – Exports the negative divergence of each voxel.
Divergence Smooth  – Exports the blurred negative divergence of each voxel.
Vorticity – Exports the length of the curl of each voxel. Can be used for whitewater shading.
Vorticity Smooth  – Exports the blurred length of the curl of each voxel. Can be used for whitewater shading.
Velocity Gradient –  Exports the length of the gradient of the velocity field.
Injector  – Exports the pressure term created by sources in Inject mode or formed during the simulation.
Liquid Surface – Exports the surface created by the simulation.
Solid Geom Type – Exports the internal geometry type in each voxel.
Hydrostatic Pressure – Exports the pressure of the liquid at each voxel due to the effect of gravity.
Voxelization Issues – Exports voxels where the solver would produce wrong results during simulation. Such voxels are near overlapping triangles, inverted normals, open edges or other geometry issues.


Using Environment Variables with Phoenix Paths

There are path environment variables in every OS, and they can be used with Phoenix FD cache file paths.

For example, to access environment variables in Windows 10 and Windows 8, follow these steps:

In Search, search for and then select: System (Control Panel).

Click the Advanced system settings link.

Click the Environment Variables... button.

In the System variables section, using Edit System Variable (or New System Variable) window, specify the value of the PATH environment variable.

Using this, you can create a path (variable), give it a name, and use it for cache files in Phoenix FD.

For example, the path D:\PhoenixFD\Cache can be given the environment variable name "Cache". In the Phoenix Simulator Output rollout, you can specify the Output Path as the following:


This will save the Phoenix cache files in D:\PhoenixFD\Cache.

Note that in order to reference environment variables, the following pattern must be used:



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