Heptagonal tegum

The heptagonal bipyramid or hedpy, also called a heptagonal dipyramid, is a bipyramid with a heptagon as the midsection, constructed as the dual of a heptagonal prism. It has 14 isosceles triangles as faces, with 2 order–7 and 7 order–4 vertices.

In the variant obtained as the dual of a uniform heptagonal prism, the side edges are $$\frac{1}{2\sin^2\frac\pi7} ≈ 2.65597$$ times the length of the edges of the base heptagon. Each face has apex angle $$\arccos\left(1-2\sin^4\frac\pi7\right) \approx 21.70194°$$ and base angles $$\arccos\left(\sin^2\frac\pi7\right) \approx 79.14903°$$. If the base heptagon has edge length 1, its height is $$\frac{\cos\frac\pi7}{\sin^2\frac\pi7} ≈ 4.78589$$.