Fields > Volume Axis >

The following section describes options in the Volume Axis Options window.

If you are creating a volume axis curve, for additional attributes, see Additional Field Attributes.

Magnitude

Specifies the strength of the volume axis field.

Attenuation

Sets how much the strength of the field diminishes from the central axis of the volume axis field.

If you set Attenuation to 1, the strength of the field diminishes in a linear manner from full strength at the central axis to zero strength at the edge of the volume axis field. Values greater than 1 make the strength of the field diminish to zero in an exponential manner—the greater the value, the more rapidly the strength decreases.

A value of 0 makes the strength remain constant from the central axis of the volume axis field to its edge (see also Invert Attenuation).

Distance

Use Max Distance

Turn this on to apply the value set in Max Distance.

Max Distance

Sets the maximum distance at which the field has an effect. You must also turn on Use Max Distance for Max Distance to take effect.

NoteThe Max Distance and Attenuation attributes operate in a special way for the Volume Axis field. For all volume axis shapes except sphere, distance (for both the Max Distance and Attenuation attributes) is defined as the distance from the volume’s central axis to the point.

For cylinder, cone, and cube, the central axis is the positive Y axis. For torus, the central axis is the ring in the center of the solid part of the torus. The sphere volume is an exception— it uses the center point, not the center axis (it works like the other fields).

This special definition of distance applies only to the Volume Axis field. It does not apply to other fields even when they are using volumes.

Volume Control Attributes

Volume Shape

Specifies the closed volume that defines the area in which the volume axis field affects particles and rigid bodies. You can choose from five volume shapes: cube, sphere, cylinder, cone, and torus.

The implicit shape of the volume axis field is displayed on the screen. You can move, rotate, scale, or shear the field.

NoteYou can’t deform the volume or use an arbitrary volume.

Volume Offset X, Y, Z

Offsets the volume axis field from the actual location of the field.

Volume Sweep

Defines the extent of the rotation for all volume shapes except cube. This can be a value from 0 to 360 degrees.

Section Radius

Defines the thickness of the solid portion of a torus volume shape.

Volume Speed Attributes

Invert Attenuation

When you turn on Invert Attenuation and you have Attenuation set to a value greater than 0, the strength of the volume axis field is strongest at the edge of the volume and diminishes to 0 at the central axis of the volume axis field (see also the Attenuation attribute on Attenuation).

Away From Center

Specifies the speed at which particles move away from the center point of cube or sphere volumes. You can use this attribute to create explosive effects.

Away From Axis

Specifies the speed at which particles move away from the central axis of cylinder, cone, or torus volumes. For torus, the central axis is the ring in the center of the solid part of the torus.

Along Axis

Specifies the speed at which particles move along the central axis of all volumes.

Around Axis

Specifies the speed at which particles move around the central axis of all volumes. When used in conjunction with a cylinder volume shape, this attribute can create swirling gaseous effects.

Directional Speed

Adds speed in the direction specified by the Direction XYZ attributes of all volumes.

Direction X, Y, Z

Moves particles in the directions specified by the X, Y, and Z axes.

TipWhen working with volumes, it’s sometimes useful to set the Conserve attribute to 0 in the particle shape. This keeps the particles within the volume. Particles will not exit the volume unless other forces act on them to make them do so. Also, see Keep particles or inside the volume.

Turbulence

The intensity of a force simulating a turbulent wind that evolves over time.

Turbulence Speed

The rate of change of the turbulence over time. The turbulence loops seamlessly every 1.0/Turbulence Speed seconds. To animate this rate attach a new time node to the time input and animate the time value on the time node.

Turbulence Frequency X, Y, Z

Controls how many repeats of the turbulence function fit inside the bounding volume of the emitter. Low values create a very smooth turbulence.

Turbulence Offset X, Y, Z

Use this option to translate the turbulence within the volume. Animating it can simulate blowing turbulent wind.

Detail Turbulence

The relative intensity of a second higher frequency turbulence. Both the speed and the frequency on this second turbulence are higher than the primary turbulence. When the Detail Turbulence is non-zero the simulation may run a bit slower, due to the computation of a second turbulence.