18-2 step prism

The 18-2 step prism is a convex isogonal polychoron and a member of the step prism family. It has 9 rhombic disphenoids and 126 phyllic disphenoids of six kinds as cells, with 30 (2 rhombic and 28 phyllic disphenoids) joining at each vertex.

Vertex coordinates
Coordinates for the vertices of an 18-2 step prism inscribed in an octadecagonal duoprism with base lengths a and b are given by: where k is an integer from 0 to 17. If the edge length differences are to be minimized, the ratio of a:b must be equivalent to 1:$$1+2\cos\frac\pi9$$ ≈ 1:2.87939.
 * (a*sin(πk/9), a*cos(πk/9), b*sin(2πk/9), b*cos(2πk/9)),