Particle Variance and Seed Parameters
Many parameters in the Particle Emission Property Editor, PType (Particle Type) Property Editor, Particle Goal Property Editor, and ExplosionOp Property Editor property editors (as well as a few others) have Var (Variance) parameters, which allow you to add variance to their associated parameter’s value.
In addition, some of these parameters also have a Seed parameter, which allows you to change the effect on the variance without changing either the parameter’s value or its Var value.
Var Parameters
The Var parameters define the range in which the random numbers are generated. Variance can be animated, allowing you to have different animations for the parameter’s variance and its value.
Variance is animated using two different Distribution methods: Uniform and Gaussian.
• With Uniform distribution, random numbers are distributed uniformly around the parameter’s value using the Variance value. The parameter will always be in the range [Value - Variance; Value + Variance], never outside of it.
This generates a random number between -1 and 1 depending on the seed, and then scale it and offset it so it ends up being distributed according to the variance we chose and around the average we set.
• With Gaussian distribution, random numbers are distributed as a bell curve around the parameter’s value using the Variance value. Most numbers will be in the range [Value - Variance; Value + Variance], but they may be outside of that range with [Value - Variance], and they will be outside of that range with [Value + Variance].
If you have the same value for both the parameter itself and the Variance parameter, different numbers result depending on the type of distribution you select. Numbers using Gaussian distribution will have greater variations than the ones using a Uniform distribution.
Seed Parameters
The seed defines which numbers will be generated in the range that the Var parameter specifies. The Seed parameters are available for some of the parameters that have a Var parameter. These parameters usually appear as text boxes without a label to the right of a Var parameter. They allow you to have very fine control over parameters, changing them slightly without having to change the parameter’s value or Var value.
All Seed parameters work only if you have a value other than zero for the Variance parameter to which it is associated.
To have an overall control over the whole simulation, you can set the Simulation Seed value in the ParticlesOp Property Editor. This adds an overall variance factor to all the parameters of the simulation that have a Var parameter, except for the size and color of the particles. Using this you can, for example, create identical particle clouds and test different results achieved by changing only the simulator seed value.
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