Location POP node

Emits particles at a location in space.

Overview

While the Source POP emits particles from existing geometry, the Location POP simply emits particles from a 3D coordinate.

If you're looking for a way to explicitly set the coordinates of existing particles, use the Position POP.

Location

System

Coordinate system of the Coordinates parameter below.

Cartesian

Specify location as X, Y, and Z coordinates.

Cylindrical

Specify location as radius, theta, and Z coordinates (where theta is the angle between the X and Y axes).

Polar

Specify location as radius, theta and phi coordinates (where phi is the angle between the X and Z axes).

Coordinates

Location in space to emit particles from.

Birth

This operator has two methods for emitting particles. You can use these methods together or separately:

• Impulse creates a certain number of particles each time the node cooks.

• Constant creates a certain number of particles per second.

Impulse Activation

Turns impulse emission on and off. Impulse emits the number of particles in the Impulse birth rate below each time the operator cooks. A value of 0 means off, any other value means on.

Impulse Birth Rate

Number of particles to emit each time the node cooks (when Impulse activation is on).

Const. Activation

Turns constant emission on and off. Impulse emits the number of particles in the Constant birth rate below each second. A value of 0 means off, any other value means on.

Const. Birth Rate

Number of particles to emit per second (when Constant activation is on).

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.

Attributes

The parameters on this tab let you control which and how attributes are initialized on the emitted particles. See the POP locals page for explanations of these variables.

Velocity

Set or add to velocity attribute.

Variance

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.

Add ID and parent attributes to the created particles.

Add the generation attribute to the created particles.

Add the origin attribute to the created particles. The origin attribute holds an arbitrary number that can help you identify the source of a particle.

Origin Index

Value for the origin attribute (when Add origin attribute is on).

Add speed attribute. In Houdini, the speed attribute is the length of the velocity vector.

Locals

TX, TY, TZ

Particle position

Examples

The following examples include this node.

AverageSpeed Example for Vector channel node

This example shows you how to calculate the average speed for each particle over a given time interval using CHOP nodes such as Vector, Trim, and Math.

WarpSpeed Example for Warp channel node

This example demonstrates how to retime a particle simulation using the Warp CHOP.

fieldforce Example for Field Force dynamics node

This example demonstrates the use of the Field Force DOP. It shows how to use a particle system to blow around smoke.

ParticleClusters Example for Cluster geometry node

This example demonstrates how you can use the Cluster SOP to create clusters of points based on their attribute values. The color SOP is also used to help visualize the clusters.

ConvertMetaballs Example for Convert Meta geometry node

This example demonstrates using the Convert Meta SOP to convert metaballs to polygons.

CopyCubes Example for Copy Stamp geometry node

This network shows the most basic example of how to use a particle system to copy geometry. A Copy SOP is used to reference a POP network (which included a Source and Drag POP) while copying a box object to every birthed particle.

Play the animation to see the result.

pscaleVOPSOP Example for Add Attribute VOP node

I attached a file that shows various ways to create the pscale attribute. It uses three key nodes: 1) Property POP to add pscale 2) Point SOP to add pscale 3) a VOP SOP to add pscale (that is tricked out to also do random offsets)

parameterVOP Example for Parameter VOP node

This example shows how inherit age as a custom attribute in to a surface shader to control opacity of particles with a ramp. It is accomplished using the Attribute Create SOP and a Parameter VOP.

ParticleVolumeCollision Example for Volume Sample VOP node

This example demonstrates how to set attributes on a particle based on the value of a volume at the particleâ€™s position.

To accomplish this, you can use a VOP POP to edit the particles, using the Volume Sample from File VOP to sample the volume.

In the example, particles are colored differently based on whether they are "in" or "out" of the volume, where "in" is defined in the example as "the value in the volume is > 0 at the position of the particle", but could easily be changed.