Resistance particle node

Calculates air or water resistance on instanced geometry.

All

Parameters

Local variables

This operator simulates the effect of wind or water resistance on the geometry instanced on particles . The resistance may push or rotate the instanced object.

The resistance is calculated on instanced geometry. If no geometry is instanced, this operator will not alter the particle.

The orientation of the geometry with respect to its direction of travel will often determine how much resistance is applied.

The instanced geometry should not be very complicated. Complex geometry will result in slower cook times with only marginally better results. Use a simplified representation of the real render geometry.

This operator modifies the acceleration and torque attributes of a particle.

Parameters

Resistance

The resistive factor of the medium against linear movement. Higher values produce more viscous (resistant) media.

Rotational

The resistive factor or the medium against rotational motion. Higher values produce more viscous (resistant) media.

This value is normally the same as the Resistance parameter. You can increase this value if you find your particle is either too tipsy, or decrease this value if the particle is too rigid.

Model

Uses either Viscous or Newtonian model for evaluating resistance.

Modify

Position and orientation	This operator affects both the position and rotation of the input particles.
Position only	This operator only the position of the input particles.
Orientation only	This operator only the rotation of the input particles.

Ray Count

This operator works by casting out a certain number of rays and seeing if they hit geometry. Geometry is only affected by the resistance if it gets hit by a ray. The higher the density of rays, the more accurate the simulation.

For geometry with fine details (like holes or thin spines), use more rays (300 or more) to make sure the geometry is hit.

Turbulence

Wind Current

A vector describing the wind direction. The direction of the vector controls the direction of the wind, and the length of the vector controls the intensity of the wind.

For example, a value of (0, 1, 0) would create wind traveling straight down. A value of (0, 2, 0) would represent wind traveling in the same direction but twice as strong.

Add Wind Noise

You can add noise to the wind, and have it change the wind direction, wind force, or both.

None	Do not add noise to the wind.
To wind magnitude only	Add noise to the wind strength, so the force of the wind varies but the direction stays constant.
To wind direction only	Add noise to the wind direction, so the direction varies but the strength stays constant.
To wind vector	Add noise to both the wind direction and strength.

Seed

Seed value for the random turbulence generator.

Turbulence

Number of iterations of fractal noise to add.

Roughness

Scale of noise added with each iteration.

Exponent

Noise attenuation exponent.

Frequency

Spatial frequency of noise field in X, Y, and Z.

Amplitude

Maximum value of noise field.

Offset

Amount to shift noise along X, Y, and Z axes.

Noise Type

Method used to generate noise. Hermite Interpolation and Improved Hermite are fastest.

Hermite Interpolation	Uses splines to interpolate values in the noise field.
Sparse Convolution	More computationally expensive, but produces noise fields free of artifacts present in the Hermite methods.
Improved Hermite	Uses a more linear interpolation than Hermite interpolation.
Alligator Noise	Provides a very different look than the other noise types.

Geometry

Object Type

Set this option to “Solid” if your object is closed (no holes or openings), otherwise set it to “Hollow”.

Hollow object (2D)	The instanced geometry is open (that is, it is flat, or has holes, or openings).
Solid object (3D)	The instanced geometry is closed (no holes or openings).

Divisions

The resistance POP needs to determine the volume distribution of the geometry for moment of inertia calculations. The volume is determined by dividing the space the geometry occupies into voxels. This parameter controls how many voxels per axis the operator uses.

The three values of this parameter are multiplied together. Do not use values higher than 50.

Object Scale

Scales the geometry up or down during resistance calculations. Larger objects are more affected by resistance than smaller ones (with the same mass).

Override Mass

Replaces any mass attributes on the input particles with the value of the Mass parameter below.

Mass

Mass to use when Override mass is on.

Override Center Of Mass

Normally, an object’s center of mass is at its origin (0,0,0). Use this parameter to manually set the center of mass for the instanced 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