If you have multiple particle clouds in a scene but don’t know which one is related to which emitter, select the particles coming from an emitter and the associated particle cloud is highlighted.
Setting Up the Particle Emission
Once you create and set up a particle cloud to define the general behavior of your particle simulation (see Creating a Particle Simulation), you can set up how the particles are emitted. As well, you can change the emitter object or add emitter other ones to the cloud.
A particle emission is composed of two things:
• The object from which the particles are emitted.
• The set of properties that define how the particles are emitted, such as their rate (amount), speed, and spread angle.
You can specify more than one emitter for a particle cloud. Generally, you can attach as many emitters you want to a particle cloud, and then create multiple particle types per emitter for different effects. To have multiple emitters for one cloud, see Adding Multiple Particle Emitters to the Same Cloud.
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If you have multiple particle clouds in a scene but don’t know which one is related to which emitter, select the particles coming from an emitter and the associated particle cloud is highlighted. |
By default, particles are emitted from the emitter object which you can move to another location in the scene. However, if you move the particle cloud (which is not recommended), the emitted particles are offset with respect to their natural emission point.
In addition to emitting particles from objects, you can also have emissions that are related to particle events (see Creating a Particle Event). In this case, the particles are emitted from other particles, depending on the type of event you’re creating.
Selecting an Emitter and Setting Up Its Particle Emission
1. Select a particle cloud.
2. Choose Modify > Particles > Set Emission from the Simulate toolbar.
3. Pick one or more objects in the scene that will act as the emitter of the particles, then right-click to end the picking session.
You can use any type of object to be an emitter except a cluster.
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You can constrain the emitter to an animated object to animate the particle flow emitted from it. |
To set up the emission properties
4. In the Emission property editor that opens, define the properties of the particle emission.
The emission properties are automatically named based on the emitter object’s name. You can enter a new name for them in the Name text box. If you modify the name of the emitter object afterwards, the emission properties are not renamed.
Emission parameters are summarized in the following illustration. For a description of each parameter, see Particle Emission Property Editor in the Properties Reference.
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• Many of these parameters have Var (variation) parameters which let you add variation to the parameter’s value. For information on this, see Adding Variation to Particles. • Any parameter with a connection icon is a mappable parameter. This means that you can modify their values using weight or texture maps (using images or sequences). For more information, see Parameter Maps. • Emissions that are created for particle events have their own Emission property page that is similar to this, but has some different options. See Emitting New Particles for more information. |
Particle Point of Origin and Direction
You can determine how the particles are emitted from the emitter object in terms of their origin of emission and their direction.
• Generation sets the point of origin from where the particles are emitted according to the geometry of the emitter object.
- Point: Particles originate from the points of the emitter object.
- Line: Particles originate from the edges (for polygons) or U/V isolines and boundaries (for NURBS) of the emitter object.
- Surface: Particles originate from the entire surface of the emitter object.
- Volume: Particles originate from within the volumetric boundaries of the emitter object.
- Fluid: Particles are emitted from the implicit fluid emitter object. This is applicable only for the Fluid operator (see Fluid).
• Direction sets the direction of particles emitted from the emitter object. Emission direction can be relative to the emitter object’s Local or Global reference or relative to the direction of the emitter object’s Normals.
Particle Amount (Rate) and Spread
Rate is the amount (density) of particles being emitted per second. The higher the value, the greater the number of particles being emitted.
You can choose to display only a percentage of this rate by setting the
Particle % value on the Simulation page in the ParticlesOp property editor.
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Set the Particle % to a low value for faster playback while editing, then to the full amount you want when you’re ready to view the final state. You can overshoot the values for Particle % by entering in a higher value, such as 200%, to double the number of particles emitted. |
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If you’re using the Fluid operator (see Fluid), the number of particles is determined by the Mean Distance parameter in the Fluid property editor, not the Rate parameter on the Emission page. The Mean Distance is not animatable, so to animate the emission rate, you can key the Size of the particles and/or the emission Speed (key them both at zero when you want to have no particles). |
Spread is the angle over which the particles are spread. The angle value you use is calculated from the point of emission and includes only “one side” of the emission.
However, the result is double the angle value to include both sides of the emission. For example, if you specify a value of 30 degrees, the particles are actually spread over an angle area of 60 degrees.
The Speed defines the speed of the particle emission in Softimage units per second.
The Speed value is limited by the Allowed Linear Velocity Range that you set on the General page in the Particle Type property editor (see Defining a Particle Type). The minimum and maximum values set the absolute range of speed that a particle is allowed to go. Setting the velocity range is a handy way to avoid extremely high or low speeds when particles are affected by natural forces.
Inherit is the percentage of velocity that the particles inherit from an animated emitter object at emission time.
Emitting Particles on Subframes (Oversampling)
Sometimes you may need to add particles between frames when, for example, you are emitting particles from a fast-moving emitter. In this case, empty spaces can occur between particle emissions, creating puffs of particles. Emitting more frequently than once every frame (oversampling) helps to create a continuous emission of particles. When you oversample the particle emission, you can specify how many times per frame you want to emit particles.
To oversample the particles
1. Open the particle cloud’s Emission property editor and click the Distribution tab.
2. In the Subframe Emission group, set these options:
- Randomize position does a random spreading of the particles between two successive positions of emission. For a given particle, the emission position is computed in 3D space at the current frame (or subframe) and the frame (or subframe) before. The particle is randomly positioned on the line joining these two points.
This lets you do oversampling without much cost to the calculation time, but you don’t have much control over how the oversampling is done.
- Steps defines how many emissions occur per frame (1 is the default). For each subframe, a certain number of particles are emitted at the locations specified by the position of the emitter at this subframe. This lets you spread the particles in a controlled manner and still have some puffs, if you like.
The Stratified emission on the Distribution page of the Emission property editor allows you to emit particles in distinct strata (layers). If you emit particles with identical speed from a grid, you’ll see distinct planes of particles; if you emit from a sphere, you’ll see concentric spheres of particles; and so on for each geometry. Because this option takes into consideration the geometry of the emitter, you need to use Surface as the Generation type (see Particle Point of Origin and Direction).
What happens normally with particle emission is that each particle is initialized with a velocity and a position. The position is derived from the emission position as specified by the emitter and the particle velocity: a random portion of the velocity is added to the position. Thus two particles that should be emitted with the same velocity from the same plane end up at two different distances from the plane because the random portion varies with each particle.
When Stratified emission is active, the random part is removed so all particles are at the same distance from the emitter.
Once you have created a particle cloud and set up the emission properties, you can easily open the Emission property editor by selecting the emitter object and choosing Modify > Particles > Edit Emission. The emitter’s associated Particle Type pages are also shown so you can edit them as well.
See Opening Particle-based Property Editors for other ways of opening specific property editors.
You can mute a particle emitter which lets you isolate and fine-tune the effects of other emitters in a scene.
The Mute option in the Emission property editor allows you to temporarily disable the emission, meaning that you can easily test a simulation or play back a scene without this emission being calculated as part of it. This is useful if you have several particle emissions in the scene, and you don’t want to have them all simulate while you’re testing one.
As well, you can animate the muting to do such things as having particle bursts being intermittently emitted.
Disconnecting Emitters from the Particle Cloud
You can easily disconnect particle emitter objects from the particle clouds to which they’re associated.
To disconnect an emitter object
1. Selected the particle, fluid, or explosion cloud to which one or more emitter objects is connected.
2. Choose Modify > Environment > Disconnect Obstacle/Force/Emitter from the Simulate toolbar. Pick the emitter objects you want to connect, then right-click to end the picking session.
Adding Multiple Particle Emitters to the Same Cloud
While you can’t emit multiple particle types from the same emitter, you can specify more than one emitter for a particle cloud, each of which can have one particle type. You can attach as many emitters as you want to a particle cloud. You can use any particle type with any emitter, one at a time.
To add emitters to a particle cloud
1. Select the particle cloud to which you want to add one or more emitters.
2. Choose Modify > Particles > Add Emission.
3. Select all the emitter objects to add to the cloud and right-click when you are finished.
In the explorer, you’ll see an emission node for each new emitter under the emitting object.
4. All emitter objects emit the same particle type until you set up a new particle type for it as described in Creating a New Particle Type.
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