The scenes in experiments U are made of small cylinders arranged into a spheric shape, yielding a stylized sea urchin — see the first image of Figure 5. At order n, there are 2n cylinders. The “urchin” scenes achieve a reasonably high level of complexity in rendering, since there are many intersections to compute, still at a moderate price in memory and scene building time.
The scenes in experiments S are decaying Sierpinski cubes of increasing order — see the second image of Figure 5. The Sierpinski cube of order n normally contains 20n small cubes. In our “decaying” version we erase 2 sub-elements out of 7 at every induction step, and apply pseudo-random rotation and scaling As a result, we obtain a slightly chaotic image made of approximatively 14.2n elementary cube.