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Concept
Geodesic polyhedron
Résumé
A geodesic polyhedron is a convex polyhedron made from triangles. They usually have icosahedral symmetry, such that they have 6 triangles at a vertex, except 12 vertices which have 5 triangles. They are the dual of corresponding Goldberg polyhedra with mostly hexagonal faces.
Geodesic polyhedra are a good approximation to a sphere for many purposes, and appear in many different contexts. The most well-known may be the geodesic domes, hemispherical architectural structures designed by Buckminster Fuller, which geodesic polyhedra are named after. Geodesic grids used in geodesy also have the geometry of geodesic polyhedra. The capsids of some viruses have the shape of geodesic polyhedra, and some pollen grains are based on geodesic polyhedra. Fullerene molecules have the shape of Goldberg polyhedra. Geodesic polyhedra are available as geometric primitives in the Blender 3D modeling software package, which calls them icospheres: they are an alternative to the UV sphere, having a more regular distribution. The Goldberg–Coxeter construction is an expansion of the concepts underlying geodesic polyhedra.
In Magnus Wenninger's Spherical models, polyhedra are given geodesic notation in the form {3,q+}b,c, where {3,q} is the Schläfli symbol for the regular polyhedron with triangular faces, and q-valence vertices. The + symbol indicates the valence of the vertices being increased. b,c represent a subdivision description, with 1,0 representing the base form. There are 3 symmetry classes of forms: {3,3+}1,0 for a tetrahedron, {3,4+}1,0 for an octahedron, and {3,5+}1,0 for an icosahedron.
The dual notation for Goldberg polyhedra is {q+,3}b,c, with valence-3 vertices, with q-gonal and hexagonal faces. There are 3 symmetry classes of forms: {3+,3}1,0 for a tetrahedron, {4+,3}1,0 for a cube, and {5+,3}1,0 for a dodecahedron.
Values for b,c are divided into three classes:
Class I (b=0 or c=0): {3,q+}b,0 or {3,q+}0,b represent a simple division with original edges being divided into b sub-edges.
Source officielle
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