ORF construction variants: (a) Examples of root contours. (b) Their corresponding ORF rings. The first contour is composed of the edges of the root facet. The second contour encloses six adjacent facets sharing a common vertex. The three other examples show stripe-contours including a string of 4, 8 and 12 adjacent facets. (c) The same ORF rings displayed with a color-mapping reflecting the spiral-wise arrangement. (d) Examples of ORF rings and their related arithmetic progressions.