9

Spin Operator 155
Inter face
The user interface appears in the parameters panel,
ontherightsideoftheParticleViewdialog.
Spin R ate—The rate 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 A xis sett ing includes options that let
youapplythespinonarandomorspecificaxis,
with optional random variation of the spin axis.
Default=Random 3D.
Random 3D—Spins each particle about an
arbitrary, random 3D axis.
World Space—Thespinaxisisspecifiedinthe
world coordinate space.
UsetheX/Y/Zsettingstospecifythespinaxis.
Particle Space—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 specif y the orientation
for all particles.
Speed Space Follow—The coordinate space for
particle orientation is determined by the particles’
direction throughout the event. Use this option
to allow particles that change direction during
the event to keep the spin axis aligned 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 specif y the orientation
for all particles.
X/Y /Z—Use these to set the spin ax is. 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 ac tual va lue doesn’t matter.
Similarly, to set the spin axis to 30 degrees (1/3
oftheangle)fromtheXaxistotheYaxis,you’d
set t he 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.