As say its name, emit particles from a geometry. For further information about particle systems, go check this part of the doc :
Particles
Simulate a particle system
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This modifier can be added over an existing particle system to make some trails. But this can also be done with
Emit
Emit a number of particles from another particle
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. Go check the
Particle Rule
Defines the behaviour of particles
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part of the doc.
Beware that number of emitted particles represents the total of emitted particles. If you put this modifier with a rate of 30 particles/seconds over a system containing millions of particles, you'll get 30 particles/second as a result.
Check this quick tutorial to see a little bit an extensive use of this modifier. This tutorial was made on an earlier version of Smode so the "place" modifier you see in use is the actual
3D Transform
Change every vertex position using scale, rotate and translate transformations
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Particles simulation speed can be adjust through their
Cue Transport
Playing parameters, position and length of the Function Cue
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.
