Houdini 16.5 Nodes Particle nodes

Stream POP node

Emit particles from areas where streams of particles mix.

On this page

This operator divides space into equal-sized partitions, and then emits particles from any partition where the density of particles from one or more streams is above a per-stream threshold. This can be used, for example, to generate sparks where two particle beams cross.

Smaller values for the Division Size parameter gives more partitions and a higher resolution; however, it also increases cooking time. Keep in mind that if you decrease the size of the partitions, you probably also want to decrease the thresholds.



Turns this node on and off. A value of 0 means off, any other value means on. This is useful to control the effect of this node with an expression .


Birth Position

Where in the partition to emit new particles when the density is above the threshold.

Division Size

Size of the partitions.

Offset of Grid

Distance to offset the partition grid from the default.


Enable Stream n

Use stream n.


Group n

Subset of the input particles to use as stream n.


Threshold n

Number of stream <n> particles required in a partition to emit a new particle.


Kill original particle n

When a new particle is emitted, kill the source particles from this stream in the partition.


Birth Probability

How many particles to emit in each partition.

Birth Group

Name of a group to put the new points into.

Preserve Group

If the Birth group already exists, append the new particles to the group instead of replacing its contents.

Life Expectancy

How long the particle will live (in seconds).

Life Variance

Particles will live the number of seconds in Life expectancy, plus or minus this number of seconds. Use 0 for no variance.


Initial Velocity

How to set the initial velocity of the emitted particles.

Use inherited velocity

Use the inherited velocity attribute as the initial velocity of the particles.

Add to inherited velocity

Add the inherited velocity attribute to the values from the Velocity and Variance parameters below.

Set initial velocity

Set the initial value of the velocity attribute using the Velocity and Variance parameters below.


Acceleration is inherited independently, if applicable.

Inherit Velocity

(When Initial velocity is Use inherited velocity or Add to inherited velocity) The proportion of the inherited velocity to use. Use 1 for the full inherited value, 0.5 to half the inherited value, and so on.


Set or add to velocity attribute.


Variance to velocity set above. The node will add +/- from 0 to this number along each axis to the Velocity parameter.

Ellipsoid Distribution

By default, the variance (if any) is distributed in a box, the size of which is determined by the Variance parameter. When this option is on, the variance is distributed in an ellipsoid instead.

Origin Index

Value for the origin attribute.



Total number of particles from enabled streams contained in the partition.


Sum of all enabled stream thresholds.


Time increment for this cook.


Birth Position.

See also

Particle nodes