The Birth Intersections operator allows you to birth new particles at places where the geometry of input objects intersects.
Start/End: controls the time range in which to birth new particles at intersection points.
Threshold: affects the density of particles birthed on two intersecting faces by multiplying the density value by the ratio between this value and the length of the overlap between the intersecting faces.
Min relative velocity: particles will only be generated on intersecting faces whose relative velocity is above this threshold. Increase this setting above 0 to ensure particles are not generated on stationary pairs of intersecting faces.
Density: controls the base number of particles to birth over each intersection, prior to adjustments made relative to the threshold value.
The number of particles birthed on any given intersecting face can be estimated as:
(density) x (length of intersection overlap / threshold).
A > A: this mode will compute intersections between objects in Geometry List A.
A > B: this mode will compute intersections between objects in Geometry List A and Geometry List B. Intersections between objects in the same group (A > A or B > B) will not be computed.
Offset: controls the amount of offset along face normals to position the birthed particles.
Enable velocity: controls whether velocity along face normals is added to birthed particles.
Velocity value: the amount of velocity along face normals to add to birthed particles.
Divergence: the angle of divergence applied to velocity vectors.