Meshes - Particle Mesh (PM)

The “Particle Mesh” engine is our fast high-quality meshing tool for standard particle fluids and has its origins in the RealFlow RenderKit. It has been developed to create meshes directly at render time and is fully multi-threaded. The main idea was to save resources, in terms of both time and disk space, because the meshes are not extracted in a separate pass as you know from RealFlow, but when you render the scene. With this trick, the mesh engine did not write a sequence of individual files to your hard disk anymore, but only uses a single file – the one that is currently required for the render process.

The quality, meshing speed and ease-of-use made the so-called “RK” mesh a big success and soon replaced the old standard particle mesh. The latter is still available in RealFlow, but only for legacy reasons.Our new “Particle Mesh” tool provides two fundamental modes: isotropic and anisotropic.

Isotropic vs Anisotropic

In fluid dynamics, meshing is of particular importance, because it creates a 3D hull around the particle cloud to represent its surface. The surface approximation is done by basic elements, such as triangles.

Isotropic methods use weighted spheres of variable influence, or metaballs. There, you create spheres with a given radius around the particles and define how strongly they can overlap or “attract” one another to form a smooth surface. A similar approach uses unweighted spheres with a global smoothing parameter to blend the elements together and create a closed surface.

All these methods are isotropic, because they only describe the surface from a set of particles with equal characteristics. Properties like curvature or particle distribution around the fluid are not taken into account. There are, of course, methods to mimic these differences in a surface's topology, but they are actually only filters to process certain parts of the mesh to achieve a sharper fluid border, or remove patterns.

Anisotropic meshes follow a completely different, much more complex approach. Here, the particles are not represented as spheres but ellipsoids, and their main axes are related to the spacial distribution of a particle's neighbours. An obvious advantage is a mesh that will match the underlying particle cloud much better.

How This Affects Your Work

When you take a look at the “Particle Mesh” node's “Mesh” panel you will see three different types: “Metaballs”, “Weighted Isotropic” and “Weighted “Anisotropic”. No matter, which mode you want to use for your current meshing task, there will always be exactly the same parameters to adjust. So, if you are familiar with the “RK” mesh engine's mode of operation from previous RealFlow versions, you will immediately know how to work with our anisotropic tool.

Although you will not recognize any differences in terms of handling and workflow, there are huge differences with regards to quality. The anisotropic mesh engine's algorithm, and its ability to analyse the fluid's surface properties, creates a mesh that really represents the fluid's characteristics, its shape and direction of flow. The fluid's borders in particular will profit from the method, because now it is possible to create naturally shaped borders without thick or rounded “edges”. In many cases, filters are no longer needed and the overall impression looks much more realistic. Even with relatively low particle counts it is now possible to extract impressive and highly detailed meshes.