nParticle output meshes
You can convert an nParticle object to a polygonal mesh, which you can then treat like any other mesh. Converting nParticles to a polygon mesh is useful for finishing liquid simulations and for creating motion blur and applying textures to rendered effects.
Using the Output Mesh attributes, you can set the resolution and quality of the resulting polygon mesh as well as select the type of polygons used to create the mesh. See Convert nParticles to polygons.
When you convert an nParticle object to polygons, you can also choose to generate per vertex data, such as per-vertex shading and per-vertex velocity. See Output mesh per-vertex shading and Create motion blur.
Output mesh per-vertex shading
You can generate per-vertex shading data when an nParticle object is converted to a polygon mesh by turning on Color Per Vertex, Opacity Per Vertex, and Incandescence Per Vertex. Per-vertex shading data is derived from the nParticle object’s per-particle color, opacity, and incandescence values.
The output mesh per-vertex data is color set data that can be applied to the polygon object like other color set data. To generate per-vertex data for your nParticle output mesh, you must set an internal Color, Opacity, or Incandescence per-particle ramp or have an expression that generates per-particle Color, Opacity, or Incandescence values. If you are emitting nParticles from a surface, you must have Inherit Color or Inherit Opacity turned on. See Inherit Color and Inherit Opacity.
See Set nParticle output mesh properties and Setting the output mesh color set.
When you convert your nParticle object to a polygon mesh, Maya generates velocity per-vertex data that can be used to create motion blur when the mesh is rendered using mental ray for Maya. Velocity Per Vertex, generates data from the nParticle object by mapping nParticle velocity values to R, G, and B color values. Velocity Per Vertex is on by default. The velocity per-vertex data is passed to the output mesh through the polySurfaceShape node’s color set named Motion Vector Color Set. By default, this color set uses the velocityPV data generated from the nParticle object.
To see motion blur in your rendered nParticle output mesh, ensure that you have Motion Blur on in your mental ray render options. See Motion Blur in the Rendering guide.