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Speed Test 233
Speed Test
Particle View (page 2–125) > Click Speed Test in an event or
add Speed Test to the particle system and then select it.
Speed Test lets the particle system check particle
speed, acceleration, or the rate of circular travel,
and branch accordingly. The test provides a
number of variants that let you test speed or
acceleration on specific axes, or simply whether
the particle is accelerating or decelerating.
Inter face
The user interface appears in the parameters panel,
ontherightsideoftheParticleViewdialog.
The first interface element is a drop-down list that
lets you choose the type of measurement to test:
•
Velocity M agnitude—Te s ts t h e p a r t icle
velocity, in system units per second, without
consideration of direction. This is the default
test type.
•
Velocity X/Y /Z—Tests the particle velocity on the
specified axis, in s ystem units p er second, us ing
the world coordinate system.
An example of this option would b e w ith
fireworks: As the particles move upward, their
velocity on the world Z axis is positive. When
the reach the top of their trajectory and begin
to move downward, their velocity on the world
Z axis slows to 0, and then b ecomes negative.
IfyouchooseVelocityZandIsLessThanTest
Va lue, and set Test Value to 0.0, you can send
particles to another event at the moment they
begin to move downward.
•
Acceleration M agnitude—Te s t s t he p a r t i cle
acceleration(changeinvelocity),insystem
units per second per second, w ithout respect
to direction.
•
Acceler ation X/Y/Z—Te s ts t he p a r t icle
acceleration (change in velocity) on the
specified axis, in system units per second per
second, u sing the world coordinate system.
•
Steer ing R ate—Tests t h e c i rcular c omp onent of
particle travel in degrees per second, without
consideration of rotation or spinning.
Fo r example, if a particle travels along a
parabolic path, its motion has both linear and
circular components. The circular component
is greatest at the top of the parabola. If a p article
travelsinafullcircleinonesecond,therateis
360; if it t ravels in a half circle, the rate is 180.
Potential usage: When a particle is forced to
turn too sharply, it might explo de or change its
type of movement. For example, missiles chase
a jet fighter, which maneuvers to elude the
missiles. The missiles are forced to change their
course rapidly, but the missile construction
cannot stand the fast change in steering, s o the
missiles blow up or disintegrat e.
Tip: You can test steering rate by setting the
part icle speed with Speed By Icon (page 2–162),
and linking the Speed By Icon operator icon
to a circular path.
•
Tru e Wh en Accel erates— Returns a True value
whentheparticlevelocityisincreasinginvalue.