Great enneagrammic retroprismatic prism

The great enneagrammic retroprismatic prism or gisterpip is a prismatic uniform polychoron that consists of 2 great enneagrammic retroprisms, 2 great enneagrammic prisms, and 18 triangular prisms. Each vertex joins 1 great enneagrammic retroprism, 1 great enneagrammic prism, and 3 triangular prisms. As the name suggests, it is a prism based on the great enneagrammic retroprism. Being a prism based on an orbiform polytope, it is also a segmentochoron.

Vertex coordinates
The vertices of a great enneagrammic retroprismatic prism, centered at the origin and with edge length 2sin(4π/9), are given by the following points, as well as the central inversions of their first three coordinates: where $$H=\sqrt{\frac{1-2\cos\frac{4\pi}9}{2-2\cos\frac{4\pi}9}}\sin\frac{4\pi}9.$$
 * $$\left(1,\,0,\,H,\,±\sin\frac{4\pi}9\right),$$
 * $$\left(\cos\left(\frac{2\pi}9\right),\,±\sin\left(\frac{2\pi}9\right),\,H,\,±\sin\frac{4\pi}9\right),$$
 * $$\left(\cos\left(\frac{4\pi}9\right),\,±\sin\left(\frac{4\pi}9\right),\,H,\,±\sin\frac{4\pi}9\right),$$
 * $$\left(-\frac12,\,±\frac{\sqrt3}2,\,H,\,±\sin\frac{4\pi}9\right),$$
 * $$\left(\cos\left(\frac{8\pi}9\right),\,±\sin\left(\frac{8\pi}9\right),\,H,\,±\sin\frac{4\pi}9\right),$$

Representations
A great enneagrammic retroprismatic prism has the following Coxeter diagrams:
 * x2s2s9/5s (full symmetry)
 * x2s2s18/5o
 * xx xo9/5ox&#x (great enneagrammic prism atop gyrated great enneagrammic prism)