Houdini 16.5 Nodes Particle nodes

Orbit POP node

Makes particles orbit a center-point.

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This operator calculates and applies forces necessary to make particles orbit around a center-point.

You can use the second input to specify the center particles, or use the parameters on the Center tab to choose a group in the first input that will specify the center.

The Center Type parameter on the Center tab let you choose how the center works:

Orbit works similarly to the Follow POP, which makes particles follow a leader or leaders.

Tip

To help visualize the effect of this operator, turn on the template flag to view the acceleration guides.

This operator modifies the following attribute: accel.

Parameters

Activation

Turns this node on and off. The node is only active if this value is greater than 0. This is useful to control the effect of this node with an expression.

Note that this is activation of the node as a whole. You can’t use this parameter to deactivate the node for certain particles.

Source Group

Only affect a group of points (created with, for example, a Group POP or Collision POP) out of all the points in the input.

Orbit

Override Axis

Use the value of the Axis parameter below instead of the orbit axis attribute if it exists on a particle.

Axis

A vector to use as the orbit axis, when Override axis is on.

Override Radius

Use the value of the Radius parameter below instead of the orbit radius attribute if it exists on a particle.

Radius

Radius of orbit (in units), when Override Radius is on.

Override Speed

Use the value of the Speed parameter below instead of the orbit speed attribute if it exists on a particle.

Speed

Speed of the orbit (in RPM), when Override Speed is on.

Scale

Scaling factor that controls how fast particles move into their proper orbit from their initial position.

Center

Center Group

Subset of points from the first input to act as centers. You can use this parameter instead of connecting the second (Center) input.

Center Type

Specifies what the particles orbit around.

Particle Spatial Center

The center of the box bounding the center particles.

Particle Center of Mass

The center of mass of the center particles.

Particle Density Center

The center of mass, with all particles having equal mass.

Center Point

Use the coordinates in each particle’s orbit center attribute (or the coordinates in the Center Point parameter below if Override Center Point is on).

Individual Particles

Each orbiting particle orbits a center particle. If you have orbit attributes on the follower particles, they will use the attribute to decide which leader to follow (using the Orbit index parameter below). Otherwise, Houdini will automatically assign followers to leaders.

Override Center Point

Use the value of the Center Point parameter below instead of the orbit center attribute if it exists on a particle, when Center Type is "Center point".

Center Point

Point to orbit around, when Center type is "Center point" and Override Center Point is on.

Orbit Index

(Available when Center type is "Individual Particles") Controls how the node interprets the orbit attribute on particles to assign satellites to centers.

Particles that do not have orbit attributes are assigned to leaders automatically, using particle order to refer to a leader.

Particle ID

The orbit attribute on the satellite particles refers to the particle ID of the center they should orbit.

Particle Order

The orbit attribute on the follower particles refers to the position of the center particle in the list of particles. In a particle system where leader particles are dying and points are being reused, this could mean the centers change as particles die (even if they are not in the center stream).

Inputs

Orbit

The particles that will be made to orbit the center or centers.

Center

The particles that define the center(s) to orbit. If you do not connect this input, you must set the Center Group parameter on the Center tab.

Locals

Standard POP local variables

AGE

The seconds a particle in the template has been alive.

AX AY AZ

Acceleration of the particle.

BBX BBY BBZ

The point’s relative position in the bounding box.

DEAD

Point is dead.

ITER

Processing iteration number.

JUSTHIT

A collision for this particle was detected (for example, by the Collision POP) during the processing of this timestep (that is, this iteration of the particle simulation). This variable is cleared at the beginning of each timestep. Note that the collision POP actually detects any collisions which would have occurred the during the previous frame.

LIFE

Percent of total life used (from 0 to 1).

LIFESPAN

Expected lifetime of particle.

MAPU MAPV MAPW

Point or vertex texture coordinates.

NPT

Total number of points.

NGRP

Total number of points in source group.

NX NY NZ

Normal vector.

PT

The point number of the currently processed point. The PT is not constant like ID; it changes based on the number of points.

RESTX RESTY RESTZ

The rest position.

SLIDING

The sliding state of the particle.

SPRINGK

Elasticity of a point.

STOPPED

Point is stopped.

STUCK

1 if particle is stuck to a collision object.

TENSION

Spring tension.

TIMEINC

Time increment.

TX TY TZ

Point position.

U V

Surface UV values.

VX VY VZ

Velocity direction.

WEIGHT

Point spline weight.

Added by Collision POP/Limit POP

DIST

Distance from particle to last collision.

HCR HCG HCB

Diffuse color at the collision point on the surface the particle collided with.

HITID

ID for last collision. You can control how this attribute is set in the Collision or Limit POP to help distinguish types of collisions.

HITTIME

The time at which the last collision occurred.

HMAPU HMAPV

The texture map UV coordinates for the surface location where the last collision occurred.

HNX HNY HNZ

The normal at the surface location where the last collision occurred.

HTX HTY HTZ

World space position of the last collision.

HU HV

The UV coordinates for the surface location where the last collision occurred.

NUMHIT

Number of times the particle has collided.

Added by Color POP

CA

Point or vertex alpha value.

CR CG CB

Diffuse point or vertex color.

Added by Property POP

ATTRACT

Attractor point.

CHARGE

Charge of the particle.

CLING

Point is clinging to geometry.

DRAG

Point drag.

FOLLOW

Leader to follow.

MASS

Point mass.

PSCALE

Particle Scale.

SCALEX SCALEY SCALEZ

Non-uniform scale.

Added by Proximity POP

NEAREST

Either the point number or id of the particle nearest to this one.

NEARESTDIST

The distance to the nearest particle.

NUMPROXIMITY

The number of particles within a specified proximity to this particle.

Added by Rotation POP

ROTA

Rotation angle.

ROTX ROTY ROTZ

Rotation axis.

Added by Source POP

GEN

Generation.

ID

ID number, which always remains constant.

ORIGIN

Original Source point was birthed from.

PARENT

Parent’s ID Number.

Added by Speed Limit POP

SPEEDMAX

Maximum speed.

SPEEDMIN

Minimum speed.

Added by Sprite POP

SROT

Sprite rotation around view axis (in degrees).

STEXU STEXV

Texture coordinate of sprite’s lower-left corner.

STEXW STEXH

Size of sprite in texture space.

SX SY

Sprite scale.

Controlled by Suppress Rule POP

SUPPPOS

Suppress default position rule.

SUPPVEL

Suppress default velocity rule.

SUPPUP

Suppress default up-vector rule.

SUPPAGE

Suppress default aging rule.

SUPPROT

1 if particle is suppressing its default rotation rule.

SUPPANGVEL

1 if particle is suppressing its default angular velocity rule.

Added by Up Vector POP

PVX PVY PVZ

Previous velocity.

UPX UPY UPZ

Up vector.

Added by Location, Source, Softbody, Split POPs

SPEED

Absolute speed of particle.

Particle nodes