Particle Flow Simulation includes several Birth operators specially designed for use in MassFX simulation:
MassFX simulation has a specific requirement for the initial placement of particles, namely that their shapes should not intersect each other. The standard Particle Flow position operators generate particle locations at random, disregarding the possibility whether particle shapes overlap. To address this requirement, the Birth Grid operator controls both the generation of the particles and their placement: two qualities that are tightly interconnected in the case of volume packing.
The Birth Group operator copies a set of mesh objects, including their positions and orientations, as particles.
The Birth Stream operator works much like the Birth operator included with the original Particle Flow system, with the added ability to set particles' birth positions (on the operator icon) and speed. It has these additional properties in order to be able to prevent new particles from colliding with existing particles, thus creating optimal conditions for a PhysX simulation.