8

Spin Operator 151
Inter face
The user interface appears in the parameters panel,
ontherightsideoftheParticleViewdialog.
Spin R ate—The r ate of revolution in degrees per
second.
Variation—The maximum amount, in degrees per
second, by which the spin rate can vary. The actual
variation is calculated once, at random, for each
part icle.
Spin Axis group
The Spin Axis setting includes options that let
youapplythespinonarandomorspecificaxis,
with optional ra ndom variation of the spin ax is.
Default=Random 3D.
Random 3D—Spins each particle about an
arbitrary, random 3D axis.
Worl d Sp ace—Thespinaxisisspecifiedinthe
world coordinate space.
UsetheX/Y/Zsettingstospecifythespinaxis.
Particle S pace—Thespinaxisisspecifiedinthe
local coordinate space of each particle.
UsetheX/Y/Zsettingstospecifythespinaxis.
Speed S pa ce—The coordinate space for particle
orientation is determined by the particles’
direction upon entering the event.
The X axis is aligned with the particle direction,
while the Z axis is perpendicular to the X axis and
ispointedupwardwithrespecttoworldspaceas
much as possible.
Use the X/Y/Z settings to specify the or ientation
for all particles.
Speed Space Follow—The coordinate space for
particle orientation is determined by the particles’
direction throughout the event. U se this option
to allow particles that change direction during
the event to keep the spin axis alig ned with their
direction.
The X axis is aligned with the particle direction,
while the Z axis is perpendicular to the X axis and
ispointedupwardwithrespecttoworldspaceas
much as possible.
Use the X/Y/Z settings to specify the or ientation
for all particles.
X/Y /Z—Use these to set the spin axis. Unavailable
for the Random 3D option. Default=0,0,1.
Range=-1.0 to 1.0.
To specify a single axis, set the corresponding
parameter to any non-zero value, and the others
to 0. A negative value flips the axis, and reverses
the direction of rotation. The numeric values
comeintoplaywhenyougivemorethanoneaxisa
non-zero value, in which case their effect is relative
to one another. For example, if you want the spin
axis to be oriented halfway between the positive
X and Y axes, you would set X and Y to the same
positive amount. The actual value doesn’t matter.
Similarly, to set the spin axis to 30 degrees (1/3
oftheangle)fromtheXaxistotheYaxis,you’d
set the Y value to twice that of the X value. For
example, X=0.2 and Y=0.4, or X=0.5 and Y=1.0.