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154 Chapter 11: Space Warps and Particle Systems
Speed S pa ce—
Thecoordinatespaceforparticle
orientation is determined by the particles’
directionuponenteringtheevent.
By default, using the Speed operator (page 2 –159)
> Along Icon Ar row option, particles are aimed
straight down when born.
Use the X/Y/Z settings to specify the orientation
for all particles.
Speed Space Follow—The coordinate space for
particle orientation is determined continually
while the particles are in the event. Thus, by
default, particles constantly reorient themselves to
“aim”inthedirectionthey’retraveling.
For example, if you add a Find Target test (page
2–218) to the end of the default Event 01, move the
target sideways, and set Rotation to Speed Space
Follow, the particles start out pointing straight
down, as oriented by the Speed operator, and
then gradually reorient themselves to point in the
direction they’re trav eling: toward the target.
Use the X/Y/Z settings to specify the orientation
forallparticles. TheDivergencesettingis
unavailable when using Speed Space Follow.
X/Y /Z—Set the basic orientation about the particles’
local axes. Unavailable with the Random 3D and
Random Horizontal options.
Divergence—Defines the range of variation (in
degrees) for particle orientation. The actual
deviation is calculated at random within this
range. Unavailable with the Random 3D or Speed
Space Follow option. Default=0.0.
Restrict Diverg[ence] To Axis—When on, lets you
use the Divergence Axis controls to set the axis
towhichdivergencewillbeapplied.Whenoff,
the software uses a random axis for each particle.
Unavailable with the Random 3D or Speed Space
Follow option. Default=off.
Divergence Ax is—Use the X/Y/Z settings to set
the axis to which divergence will be applied.
Default=1,0,0. Range=-1.0 to 1.0.
To specify one of the world axes, set the
corresponding parameter to any non-zero value,
and the others to 0. A negative value flips the axis.
The numeric values come into play when you want
to use an axis that’s not aligned with the X, Y, or Z
axis. In that case, you specify multiple non-zero
values whose effect is relative to one another.
For example, if you want the axis to be oriented
halfway between the positive X and Y axes, you
wouldsetXandYtothesamepositiveamount.
The actual value doesn’t matter . Similarly, to set
the axis to 30 degrees (1/3 of the angle) from t he
X axis to t he Y axis, you’d set the Y va lue to twice
that of the X value. For example, X=0.2 and Y=0.4,
or X=0.5 and Y=1.0.
Uniqueness group
The Uniqueness setting affects the randomization
of orientation with the Random 3D and Random
Horizontal options, a nd also Divergence.
Seed—Specifies a randomization value.
New—Calculates a new seed using a randomization
formula.
Spin Operator
Partic le View (page 2–125) > Click a Spin operator in a n
event or add a Spin operator to the particle system and
then select it.
The Spin operator g ives an angular velocit y to
particles in an event, with optional random
variation. Spin is applied once per event per
particle, except when using the Speed Space Follow
option; however, the settings can be animated.
To simply specify particle orientation, use the
Rotation operator (page 2–153).