9

Object Motion Inheritance Rollout 269
Spin Ax is Controls group
These options determine the spi n axis for the
particles, and provide a par tial method of applying
motion blur to the particles.
Random—Thespinaxisforeachoftheparticles
is random.
Direction of Travel/Mblur—(Not available with the
Blizzard particle system.) Rotates the particles
about a vector formed by the direction in which
they’re moving. This option also lets you apply
aformofmotionblurtotheparticlesbyusing
the Stretch spinner. For further information, see
Achieving Particle Motion Blur (page 2–240).
Stretch—When greater than 0, the particles stretch
along the travel axis, depending on their speed.
Specifically, the Stretch value specifies the percent
of their leng th per each unit of the Speed setting
(in the Particle Motion group). Thus, if you set
Stretch to 2 while Speed is set at 10, the particles
are stretched 20 percent longer than their original
size along the axis of their travel. This spinner
is available only when you choose Direction of
Travel/Mblur.
Note: For best results w hen using Stretch, you
should also assign the Particle MBlur map as
an opacity m ap of the material assigned to the
particle system.
User Defi ned—Uses a vector defined in the three X,
Y, and Z axis spinners.
X/Y /Z Axis—Specifies the spin vector of the X, Y, or
Z axis, respect ively. These spinners are available
only w hen User Defined is chosen.
Variation—The amount, in degrees, by which
thespinaxisofeachparticlemayvaryfromthe
specified X Axis, Y Axis, and Z Axis settings. This
spinner is available only when you choose User
Defined.
Interpar ticle Collisions group
These options enable collisions between particles,
and control how the collisions occur. Note that this
involves intensive calculation, particularly when
large numbers of particles are involved.
Enable—Enablesinter-particlecollisionsinthe
calculation of the particle movements.
Calc Intervals Per Frame—The number of
intervalsperrenderinginterval,duringwhich
an inter-particle collision test is conducted. The
higher the value, the more accurate the simulation,
but the slower the simulation will run.
Bounce—The degree to which speed is recovered
after a collision.
Variation—Thepercentageofrandomvariationof
theBouncevalue,appliedtotheparticles.
Object Moti on I nheri tance R ollout
Create panel > Geometry button > Choose Particle
Systems from the drop-down list. > Object Type rollout
> SuperSpray/Blizzard/Parray/PCloud > Object Motion
Inheritance rollout
Select a SuperSpray/Blizzard/Parray/PCloud emitter. >
Modify panel > Object Mo tion Inheritance rollout
Each particle’s position and direction of movemen t
are determined by the position and orientation of
the emitter at the time the particle is created. If the
emitter is moving through the scene, p articles are
scattered a long the emitter’s path.
Use these options to affect the motion of the
particles by the motion of the emitter.
Procedure
Ex ample: To obser v e object motion inher ita nce:
1.
Create a Super Spray particle system.
2. Animate the emitter moving sideways
(perpendicular to the direction of the par ticle
stream) between f rames 1 and 15.