EC - Hybrido Domains

Grid domains support a wide variety of file formats and it is also possible to bake the speed and vorticity information of a Hybrido simulation into 32 bit HDR files. The standard format is RPC - the RealFlow Particle Cache. These files store the particle data of the Hybrido fluid, while the associated fields are saved in GFC files by default.

Fields cache (.gfc)

This is a native RealFlow format that contains the fluid's entire field information. This data is also required to resume a Hybrido simulation and create secondary elements. In contrast to Field3D, this format does not provide compression, but it is faster to write. GFC files are stored in the project's “grid” folder.

Particles cache (.rpc)

RPC is another RealFlow-specific format, but fully documented and supported by the various exchange plugins. It stores the Hybrido fluid's particle data and can replace BIN files. You can choose which data channels you want to export, but please bear in mind that Hybrido fluids do not calculate normals and vorticity by default. These options have to be activated in the domain's “Particle Channels” panels.

Fields cache -Field3d- (.f3d)

Field3D is an open source library developed by Sony Picture Imageworks and can store voxel data. Voxels are 3-dimensional volume elements and used when a certain space (= domain) has to be subdivided into a grid of cells. The F3D format can fully replace or substitute the GFC format, but it takes longer to write a F3D file. F3D files are stored in the “grid” directory of your project’s folder. There are some more advantages: with F3D files you can choose which field data (velocity, distance or displacement) you want to store and it supports ten compression levels. It is fully documented and very common in the VFX industries. Since it is an open source library, C++ programmers will be able to write their own importers. The RealFlow-specific meta data can be found in RealFlow's application folder on your hard disk:

docs > format > field3d.pdf

Fields cache -OpenVDB- (.vdb)

OpenVDB is an open source library developed by DreamWorks Animation and can store voxel data. The format can fully replace RealFlow's native GFC and it is possible to resume from interrupted simulations or create secondary elements from VDB files. RealFlow's fields have to be converted into VDB-compatible data and therefore it takes longer to write VDB files. OpenVDB supports compression. Since the format is an open source C++ library, TDs are able to write their own import tools. The RealFlow-specific meta data and many additional information can be found here. Please bear in mind that RealFlow's OpenVDB implementation is tied to Houdini's axis setup.

RealFlow's Graphs engine offers nodes to load, write, and visualize information from VDB files. Examples and downloadable graphs are available here.

Particles cache -Alembic- (.abc)

Alembic files for grid domains support multiple channels from which you can choose when you expand the “Particle cache (a.bc) branch. In contrast to standard SPH fluids, the particles from grid fluids only carry some magnitudes: position, velocity, texture, vorticity, normal, and id. RealFlow's implementation of the Alembic format supports 10 different compression levels from 0 to 9. A higher value indicates a stronger compression. As usual, the compression requires some time and so the saving process becomes slower, but it is more resource-friendly.

Particles cache -Arnold- (.ass)

This is the scene description format of Solid Angel's Arnold render engine. You can export simulation data to native ASS files for direct use inside Arnold.

Particles (.pxy)

“PXY” is an internal format that can be used with RealFlow and the RealFlow RenderKit. PXY is a proxy format and only stores a particle’s Id, position and velocity. Depending on the adjusted quality level under “Options”, some particles are left out during storage, but it is perfectly suited for high volumes of particles. There are five quality levels (best – draft) to choose from. They can be seen/adjusted with a double-click on the “Best” option right of the export resource's name.

Particles (.bin)

It is possible to “convert” Hybrido's marker particles inside the cells into RealFlow's standard BIN file format. This way it is, for example, possible to send the particles to the RealFlow RenderKit's mesh engine and perform the meshing process directly at render time. BIN is RealFlow’s most common particle file format. It contains all relevant position and physical data, such as density or pressure. BIN files can be read by any plugin available for 3D programs and they are accessible via Python scripting for storing customized particle files. BIN files are fully supported by RealFlow’s import and export filters and all available plugins.

Particles -Krakatoa- (.prt)

Thinkbox Software’s Krakatoa™ is a volumetric particle rendering system for 3DStudio Max. RealFlow is capable of writing native PRT files for direct use inside Krakatoa™. The PRT format also supports a wide variety of individual channels for all standard particle attributes. You can activate and deactivate them on demand by simply ticking the checkboxes.

Displacement texture (.tif)

A grid fluid's displacement can either be added to the grid mesh and/or stored separately as a TIF file sequence. These images can be loaded to your 3D program and used to reconstruct the surface structure. The RealFlow RenderKit provides a comfortable tool to quickly apply the maps to a mesh or any other object. Since the coloured displacement maps are always stored in 16 bit mode, the only output format is TIFF. Greyscale TIFFs are stored with a depth of 8 bit depending on your settings (“YYY” or “XYZ”). Before you can make use of this feature, it is necessary to activate it under the grid domain’s settings:

Hybrido Domain node > Node Params > Ocean Statistical Spectrum > Calculate > Yes

Velocity texture (.exr)

It is also possible to export maps based on the grid fluid's velocity values. The textures are generated from the fluid surface and use a top projection method. This feature only supports the EXR format. The maps can found in the project's “images” folder. In these files, the velocity is colour-coded and the RGB values represent the X, Y and Z components of the stored velocities. Additionally, you will find an Alpha channel that contains the velocity's magnitude. The map size can be adjusted in the "Option" column.

Vorticity texture (.exr)

It is also possible to export maps based on the grid fluid's vorticity values. The textures will be generated from the fluid surface and use a top projection method. This feature only supports the TIF format. The maps can found in the project's “images” folder. In these files, the vorticity is colour-coded and the RGB values represent the X, Y and Z components of the stored vorticity. Additionally, you will find an Alpha channel that contains the vorticity's magnitude. The map size can be adjusted in the "Option" column. Before the fluid's vorticity information can be turned into maps, the feature has to be enabled under

 Hybrido Domain node > Node Params > Particle Channels > Vorticity > Yes