Noise module that outputs 3-dimensional MultiFractal noise. The multifractal algorithm differs from the Fractal brownian motion in that perturbations are combined multiplicatively and introduces an offset parameter. The perturbation at each frequency is computed as in the fBM algorithm, but offset is finally added to the value. The role of offset is to emphasize the final perturbation value. Multiplicative combination of perturbation, in turn, emphasizes the "mountain-like-aspect" of the landscape, so that between mountains a sort of slopes are generated (From http://meshlab.sourceforge.net/wiki/index.php/Fractal_Creation )