Position particle node

Explicitly sets a particle’s position.

All

Parameters

Local variables

By default, Houdini moves particles automatically from frame to frame according to their velocity. This operator lets you position the particles directly.

Note

The default movement will also be applied unless you turn the default movement rule off with a Suppress Rule POP.

You can use the current position variables ($TX, $TY, and $TZ) in an expression to make the new position relative to the current position.

For example, to move the particle by its velocity scaled by the Time Increment (since velocity is distance-per-second), use the following Vector expression:

vector3($TX, $TY, $TZ) + $TIMEINC * vector3($VX, $VY, $VZ)

The position can be evaluated either in component form or as a vector.

This operator modifies: position (which is not actually a point attribute).

Parameters

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

Apply Motion

To all points	Set the position of all particles.
To moving points	Only set the position of particles which are currently in motion. Specifically, this excludes any stopped, stuck or dying particles.

Position/Path/Reference

Position	Position the particle using coordinates.
Path	Position the particle along a path .
Reference	Position the particle in the local space of an object.

Param

Position

Position of the particle.

Path

Use the parameters on this tab to position the particle at a point along an existing path.

Geometry Source

Specifies the SOP to use.

Use Parameter Values	Use the SOP specified in the SOP parameter below.
Use First Context Geometry	Use the SOP connected to the POP network’s first input.
Use Second Context Geometry	Use the SOP connected to the POP network’s second input.
Use Third Context Geometry	Use the SOP connected to the POP network’s third input.
Use Fourth Context Geometry	Use the SOP connected to the POP network’s fourth input.

SOP

Path to the SOP (when Geometry source is set to Use Parameter Values).

Ignore Transform Object

Particles normally use the object space of the SOP being cooked. Turn this parameter on to not transform into the space of the cooking SOP.

Position

Position along the path. 0 is the starting point and 1 is the ending point. A value higher than 1 wraps around (according to the End option parameter below), allowing multiple trips along the path.

End Option

Choose whether to restart at the beginning or reverse direction when the value of Position parameter goes past the end of the path.

Cycle	Wrap back to the start of the path.
Reverse	Reverse direction and travel back along the path the other way.

Reference

Object

Path to the reference object.

Local variables

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.

Usages in other examples

Example name	Example for
BounceSplit	Collision particle node	Load \| Launch
OrbitAlternate	Orbit particle node	Load \| Launch
NewGroupies	Follow particle node	Load \| Launch
Lemmings	Follow particle node	Load \| Launch
FlockOnPath	Follow particle node	Load \| Launch
NewGroupiesRavage	Follow particle node	Load \| Launch