Houdini 16.5 Nodes Particle nodes

Proximity POP node

Sets attributes on and/or creates groups of particles based on which other particles are nearby.

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This operator sets attributes on the input particles that record which other particles are closest and how far away they are.

You can also use groups containing the particles nearby (within a certain distance of) each particle. The groups are created by taking the value of the Group Name Root parameter and appending the ID of the particle the group corresponds to.

This operator modifies the following attributes: nearest, nearestdist, and numproximity.

Tip

Note the option Use point numbers instead of IDs. Point numbers are reused, while a particles ID is unique within the simulation and is not re-used. You might want to double-check this if the numbers you are getting do not seem right.

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.

Candidate Group

Compare against a different subset of the input particles from those specified by the Source Group parameter. Useful to find the nearest neighbor from a particular group, for example.

Add Nearest Neighbor Attribute

Sets the nearest attribute on each input particle to the ID of the nearest particle.

Add Nearest Distance Attribute

Sets the nearestdist attribute on each input particle to the distance to the nearest particle.

Add Number in Proximity Attribute

Sets the numproximity attribute on each input particle to the number of particles within the distance defined by the Proximity Radius parameter below.

Create Proximity Particle Groups

When this option is on, the operator creates new particle groups corresponding to each input particle, containing the particles closer than the Proximity Radius to that particle.

Create Groups For

Only use a subset of the input particles (created with, for example, a Group POP or Collision POP) when filling the new groups of nearby particles.

Group Name Root

The base name of the new groups created by this particle. The operators names the groups by appending the ID (or point number, if Use point numbers instead of IDs is on below) of the source particle to this base name.

Include Self in Proximity Groups

Include the source particle in the proximity group.

Proximity Radius

Distance within which other particles are grouped.

Use Point Numbers Instead of IDs

Use the point number instead of IDs to indicate particles. IDs are unique to each individual particle, while point numbers refer to a position in the list of particles. In a particle system where particles are dying and points are being reused, this could mean the "nearest" particle could change as particles die (even if they're not within the Proximity Radius.

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