User Manual

To determine if a particle is in the interior of an object, a ray is cast from infinity through that
particle and then out to -infinity. The Winding Ray Direction determines which direction this ray
is cast in. Each time a surface is pierced by the ray, it is recorded and added onto a total to
generate a winding number. Going against a surfaces normal counts as +1, and going with the
normal counts as -1.
The Winding Rule is then used to determine what is inside/outside. For example, setting the
Winding Rule to Odd means that only particles with odd values for the winding number are kept
when creating the particles. The exact same approach is used to ensure that polylines that
intersect themselves are closed properly.
For example, the following node tree and image show two image planes being used as a mesh
region for particle creation.
By setting the region’s Winding Ray Direction to the Z (blue) axis, this mesh can then be treated
as a closed volume for purposes of particle creation, as pictured below.
Limit By ObjectID
Selecting this checkbox allows the Object ID slider to select the ObjectID used as part of
the region.
Chapter – 103 Particle Nodes 2323