Dual hemipolyhedra

In geometry, a hemipolyhedron is a uniform star polyhedron some of whose faces pass through its center. These "hemi" faces lie parallel to the faces of some other symmetrical polyhedron, and their count is half the number of faces of that other polyhedron - hence the "hemi" prefix.[1]

The prefix "hemi" is also used to refer to certain projective polyhedra, such as the hemi-cube, which are the image of a 2 to 1 map of a spherical polyhedron with central symmetry.

Wythoff symbol and vertex figure

Their Wythoff symbols are of the form p/(p − q) p/q | r; their vertex figures are crossed quadrilaterals. The vertex configuration is p/q.2r.p/(p − q).2r. The 2r-gon faces pass through the center of the model. The p/(p − q) notation implies a {p/q} face turning backwards around the vertex figure.

The nine forms, listed with their Wythoff symbols and vertex configurations are:

3/2 3 | 2
(p/q = 3, r = 2)
3/2 3 | 3
(p/q = 3, r = 3)
Small icosihemidodecahedron
3/2 3 | 5
(p/q = 3, r = 5)
Great icosihemidodecahedron
3/2 3 | 5/3
(p/q = 3, r = 5/3)
Small dodecahemicosahedron
5/3 5/2 | 3
(p/q = 5/2, r = 3)
4/3 4 | 3
(p/q = 4, r = 3)
Small dodecahemidodecahedron
5/4 5 | 5
(p/q = 5, r = 5)
Great dodecahemidodecahedron
5/3 5/2 | 5/3
(p/q = 5/2, r = 5/3)
Great dodecahemicosahedron
5/4 5 | 3
(p/q = 5, r = 3)


Only the octahemioctahedron represents an orientable surface; the remaining hemi polyhedra have non-orientable or single-sided surfaces.

Duals of the hemipolyhedra

Since the hemipolyhedra have faces passing through the center, the dual figures have corresponding vertices at infinity; properly, on the real projective plane at infinity.[2] In Magnus Wenninger's Dual Models, they are represented with intersecting prisms, each extending in both directions to the same vertex at infinity, in order to maintain symmetry. In practice the model prisms are cut off at a certain point that is convenient for the maker. Wenninger suggested these figures are members of a new class of stellation figures, called stellation to infinity. However, he also suggested that strictly speaking they are not polyhedra because their construction does not conform to the usual definitions.

There are 9 such duals, sharing only 5 distinct outward forms, four of them existing in outwardly identical pairs. The members of a given identical pair differ in their arrangements of true and false vertices (a false vertex is where two edges cross each other but do not join). The outwards forms are:

Tetrahemihexacron Octahemioctacron
and hexahemioctacron
Small icosihemidodecacron
and small dodecahemidodecacron
Great dodecahemidodecacron
and great icosihemidodecacron
Great dodecahemicosacron
and small dodecahemicosacron
3 intersecting infinite square prisms 4 intersecting infinite hexagonal prisms 6 intersecting infinite decagonal prisms 6 intersecting infinite decagrammic prisms 10 intersecting infinite hexagonal prisms

Relationship with the quasiregular polyhedra

The hemipolyhedra occur in pairs as facetings of the quasiregular polyhedra with four faces at a vertex. These quasiregular polyhedra have vertex configuration m.n.m.n and their edges, in addition to forming the m- and n-gonal faces, also form hemi-faces of the hemipolyhedra. Thus, the hemipolyhedra can be derived from the quasiregular polyhedra by discarding either the m-gons or n-gons (to maintain two faces at an edge) and then inserting the hemi faces. Since either m-gons or n-gons may be discarded, either of two hemipolyhedra may be derived from each quasiregular polyhedron, except for the octahedron as a tetratetrahedron, where m = n = 3 and the two facetings are congruent. (This construction does not work for the quasiregular polyhedra with six faces at a vertex as their edges do not form any regular hemi-faces.)[1]

Since the hemipolyhedra, like the quasiregular polyhedra, also have two types of faces alternating around each vertex, they are sometimes also considered to be quasiregular.[1]

Quasiregular polyhedron
Hemi-faces (h-gons) Hemipolyhedron with m-gons discarded
m.h.m/m - 1.h
Hemipolyhedron with n-gons discarded
n.h.n/n - 1.h
m = 3, n = 3
squares Tetrahemihexahedron
m = 3, n = 4
hexagons Cubohemioctahedron
m = 3, n = 5
decagons Small dodecahemidodecahedron
Small icosihemidodecahedron
m = 5, n = 5/2
hexagons Small dodecahemicosahedron
Great dodecahemicosahedron
Great icosidodecahedron
m = 3, n = 5/2
decagrams Great dodecahemidodecahedron
Great icosihemidodecahedron

Here m and n correspond to p/q above, and h corresponds to 2r above.


  • (Wenninger models: 67, 68, 78, 89, 91, 100, 102, 106, 107)
  • Har'El, Z. Zvi Har’El (Page 10, 5.2. Hemi polyhedra p p'|r.)

External links

  • Stella Polyhedral Glossary
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.