Advect Points node

This node will advect the points in a particle system along a velocity field. The first thing you need is a particle system to use. Node inputs are:

• Particle System - Particle system to advect
• Velocity Grid - This must be a vector-valued VDB primitive. You can use the Vector Merge node to turn a vel.[xyz] triple into a single primitive
• Closest Point Grid -  Used for projection and constrained advection

In the node's panel, the controls are as follows:

• Type - Three types are proposed:
  • Advection - Move the point along the velocity field
  • Projection - Move the point to the nearest surface point
  • Constrained Advection - Move the along the velocity field, and then project using the closest point field. This forces the particles to remain on a surface
• Integration - Later options in the list are slower but better at following the velocity field
• Iterations - Number of times to try projecting to the nearest point on the surface. Projecting might not move exactly to the surface on the first try. More iterations are slower but give a more accurate projection
• Steps - How many times to repeat the advection step This will produce a more accurate motion, especially if large time steps or high velocities are present
• Add Particles - At each frame add the input particles to the advection
• Lifespan - How many frames the advected points will live for