# Position POP node

Explicitly sets a particle’s position.

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

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 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.

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.

## 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.

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

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.

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.

CA

Point or vertex alpha value.

CR CG CB

Diffuse point or vertex color.

ATTRACT

Attractor point.

CHARGE

Charge of the particle.

CLING

Point is clinging to geometry.

DRAG

Point drag.

FOLLOW

MASS

Point mass.

PSCALE

Particle Scale.

SCALEX SCALEY SCALEZ

Non-uniform scale.

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.

ROTA

Rotation angle.

ROTX ROTY ROTZ

Rotation axis.

GEN

Generation.

ID

ID number, which always remains constant.

ORIGIN

Original Source point was birthed from.

PARENT

Parent’s ID Number.

SPEEDMAX

Maximum speed.

SPEEDMIN

Minimum speed.

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.

PVX PVY PVZ

Previous velocity.

UPX UPY UPZ

Up vector.

Added by Location, Source, Softbody, Split POPs

SPEED

Absolute speed of particle.