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Speed By Surface O perator 167

• Particle Age—Any keys set for par ameters are

applied at the corresponding frames of each

particle’s existence.

•

Event Dura tion—Any keys set for parameters

are applied to each particle relative to the f rame

at which it first enters the event.

Icon Anim atio n group

The software can begin applying animation of the

Speed By Icon operator icon to all particles as of

the star t frame of the animation or t he first f rame

of the current event, or to each particle based on

its age. For an explanation, see Animation Offset

Keying g roup (page 2–158).

Sync B y—Choose the t ime frame for applying

animation of the icon to the particles:

•

Absolute Time—Any keys set for icon motion

are applied at the actual frames for which

they’re set.

•

Particle Age—Any keys set for icon motion are

applied at the corresponding frames of each

particle’s existence.

•

Event Duration—Any keys set for icon motion

are applied to each particle relative to the f rame

at which it first enters the event.

Icon Size—Sets the size of the operator icon. This

setting is for visibility only ; it doesn’t affect particle

behavior.

Uniqueness group

The Uniqueness setting enables randomization of

the speed variation range.

Seed—Specifies a randomization value.

New—Calculates a new seed using a randomization

formula.

Speed By Surface Operator

Particle View (page 2–125) > Click Speed By Surface in an

event or add a Speed By Surface operator to the particle

system and then select it.

The Speed By Surface operator lets you control

particle speed and direction with any object or

objects in the scene. This is in contrast to the

default Speed operator (page 2–159),whichuses

theParticleFlowicontocontrolparticlespeedand

direction. Speed By Surface also provides options

for cont rolling speed by materials in the scene, and

continuous speed control.

Typically, you use Speed By Surface to assign speed

and direct ion characteristics based on the objects

used as emitters with the Position Object oper a t or

(page 2–148). That is, you assig n the same objects

as emitters with Position Object and as Surface

Geometry objects with Speed By Surface.

Tip: For greater control over particle motion on

the surface, apply a Speed operator (page 2–159)

beforetheSpeedBySurfaceoperatorinthesame

event. Use the Speed operator to specify particle

direction on the surface, and the Speed By Surface

operator to adjust the vertical component of the

speed vector to follow the contour of the surface.