FractalSum is the simplest form of fractal functions summing up a few octaves
of the noise value with an ever decreasing (0 < roughness < 1) amplitude
lacunarity = 2.0f is the classical octave distance
Note: though noise basis functions are generally designed to return value
between -1..1, there sum can easily be made to extend out of this range. To
handle this is up to the user.
Fields inherited from class com.jme3.terrain.noise.basis.Noise