9

Speed Operator 161
Inter face
The user interface appears in the parameters panel,
ontherightsideoftheParticleViewdialog.
Speed—Theparticlespeedinsystemunitsper
second. Default=300.
ApositiveSpeedvaluemovestheparticlesinthe
direction determined by the Direction setting; a
negative Speed value moves the particles in the
opposite direction.
Note: Speed sets each particle’s speed once only:
whentheparticleenterstheevent(orisborn,
in the case of a birth event). If you animate the
Speed value, particle speed does not vary: rather,
each par ticle is given a constant speed equal to t he
current Speed value when it enters the event.
Variation—The amount by w hich particle speed
can vary, in system units per second. Default=0.0.
To obtain each part icle’s speed, the system
multipliestheVariationvaluebyarandomnumber
between -1.0 and 1.0, and then adds the result to
the Speed va lue. For example, if Speed=300 and
Variation=100, then each particle’s speed would
be b etween 200 and 400.
Direction group
The Direction drop-down list lets you specify
which way the particles go after they’re born.
Default=Along Icon Arrow. In most cases,
the actual direction also depends on the icon
orientation. The primary exception is when
Position > Location is set to Pivot.
Par ticle movement is always in a s traight line
unless influenced by other factors.
Along Icon Ar row—Particles move parallel to the
icon arrow. Rotate the icon to change the direction.
Icon Center Out—Each particle moves along an
imaginary line dr awn between the particle’s
location and the icon center.
With the f lat icon types (Rectang le and Circle),
this results in all the particles moving in one
plane, unless you increase Divergence above 0.0.
Withiconsthathaveheight(BoxandSphere),the
particles move outward in three dimensions.
Particlesatthecenter,asisthecasewhenthe
P osition operator’s Location parameter is set to
Pivot, arbitrarily move a long the world X axis.
Icon Arrow Out—Each particle moves along an
imaginary line dr awn between the particle’s
location and the icon arrow. The line is
perpendicular to the icon arrow, which is
considered an infinite line for this purpose.
With the f lat icon types (Rectang le and Circle),
this results in all the particles moving in one
plane, unless you increase Divergence above 0.0.
Withiconsthathaveheight(BoxandSphere),the
particles move outward in a cylindrical formation.
Random 3D—Particles move in all directions. This
option is affected by the Uniqueness setti ng.
Random Horizontal—Each particle moves in a
random horizonta l direction; that is, parallel to
the world XY plane. This option is affected by the
Uniqueness setting.
Inher it Previous—U ses the current direction of
motion.