Bicupola (geometry)

Last updated
Set of bicupolae
Cuboctahedron.svg
Faces 2n triangles,
2n squares
2 n-gons
Edges 8n
Vertices 4n
Symmetry group Ortho: Dnh, [2,n], *n22, order 4n
Gyro: Dnd, [2+,2n], 2*n, order 4n
Properties convex
The gyrobifastigium (J26) can be considered a digonal gyrobicupola. Gyrobifastigium.png
The gyrobifastigium (J26) can be considered a digonal gyrobicupola.

In geometry, a bicupola is a solid formed by connecting two cupolae on their bases.

Contents

There are two classes of bicupola because each cupola (bicupola half) is bordered by alternating triangles and squares. If similar faces are attached together the result is an orthobicupola; if squares are attached to triangles it is a gyrobicupola.

Cupolae and bicupolae categorically exist as infinite sets of polyhedra, just like the pyramids, bipyramids, prisms, and trapezohedra.

Six bicupolae have regular polygon faces: triangular, square and pentagonal ortho- and gyrobicupolae. The triangular gyrobicupola is an Archimedean solid, the cuboctahedron; the other five are Johnson solids.

Bicupolae of higher order can be constructed if the flank faces are allowed to stretch into rectangles and isosceles triangles.

Bicupolae are special in having four faces on every vertex. This means that their dual polyhedra will have all quadrilateral faces. The best known example is the rhombic dodecahedron composed of 12 rhombic faces. The dual of the ortho-form, triangular orthobicupola, is also a dodecahedron, similar to rhombic dodecahedron, but it has 6 trapezoid faces which alternate long and short edges around the circumference.

Forms

Set of orthobicupolae

Symmetry PictureDescription
D2h
[2,2]
*222
Digonal orthobicupola.png Orthobifastigium or digonal orthobicupola: 4 triangles (coplanar), 4 squares. It is self-dual
D3h
[2,3]
*223
Triangular orthobicupola.png Triangular orthobicupola (J27): 8 triangles, 6 squares; its dual is the trapezo-rhombic dodecahedron
D4h
[2,4]
*224
Square orthobicupola.png Square orthobicupola (J28): 8 triangles, 10 squares
D5h
[2,5]
*225
Pentagonal orthobicupola.png Pentagonal orthobicupola (J30): 10 triangles, 10 squares, 2 pentagons
Dnh
[2,n]
*22n
n-gonal orthobicupola: 2n triangles, 2n rectangles, 2 n-gons

Set of gyrobicupolae

A n-gonal gyrobicupola has the same topology as a n-gonal rectified antiprism, Conway polyhedron notation, aAn.

Symmetry PictureDescription
D2d
[2+,4]
2*2
Gyrobifastigium.png Gyrobifastigium (J26) or digonal gyrobicupola: 4 triangles, 4 squares
D3d
[2+,6]
2*3
Cuboctahedron.png Triangular gyrobicupola or cuboctahedron: 8 triangles, 6 squares; its dual is the rhombic dodecahedron
D4d
[2+,8]
2*4
Square gyrobicupola.png Square gyrobicupola (J29): 8 triangles, 10 squares
D5d
[2+,10]
2*5
Pentagonal gyrobicupola.png Pentagonal gyrobicupola (J31): 10 triangles, 10 squares, 2 pentagons; its dual is the rhombic icosahedron
Dnd
[2+,2n]
2*n
n-gonal gyrobicupola: 2n triangles, 2n rectangles, 2 n-gons

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Johnson solid 92 non-uniform convex polyhedra, with each face a regular polygon

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Square orthobicupola

In geometry, the square orthobicupola is one of the Johnson solids (J28). As the name suggests, it can be constructed by joining two square cupolae (J4) along their octagonal bases, matching like faces. A 45-degree rotation of one cupola before the joining yields a square gyrobicupola (J29).

Square gyrobicupola

In geometry, the square gyrobicupola is one of the Johnson solids (J29). Like the square orthobicupola (J28), it can be obtained by joining two square cupolae (J4) along their bases. The difference is that in this solid, the two halves are rotated 45 degrees with respect to one another.

Triangular orthobicupola Johnson solid with 14 faces

In geometry, the triangular orthobicupola is one of the Johnson solids. As the name suggests, it can be constructed by attaching two triangular cupolas along their bases. It has an equal number of squares and triangles at each vertex; however, it is not vertex-transitive. It is also called an anticuboctahedron, twisted cuboctahedron or disheptahedron. It is also a canonical polyhedron.

Elongated triangular orthobicupola Johnson solid with 20 faces

In geometry, the elongated triangular orthobicupola or cantellated triangular prism is one of the Johnson solids. As the name suggests, it can be constructed by elongating a triangular orthobicupola by inserting a hexagonal prism between its two halves. The resulting solid is superficially similar to the rhombicuboctahedron, with the difference that it has threefold rotational symmetry about its axis instead of fourfold symmetry.

Elongated triangular gyrobicupola

In geometry, the elongated triangular gyrobicupola is one of the Johnson solids (J36). As the name suggests, it can be constructed by elongating a "triangular gyrobicupola," or cuboctahedron, by inserting a hexagonal prism between its two halves, which are congruent triangular cupolae (J3). Rotating one of the cupolae through 60 degrees before the elongation yields the triangular orthobicupola (J35).

In geometry, a quasiregular polyhedron is a uniform polyhedron that has exactly two kinds of regular faces, which alternate around each vertex. They are vertex-transitive and edge-transitive, hence a step closer to regular polyhedra than the semiregular, which are merely vertex-transitive.

A pseudo-uniform polyhedron is a polyhedron which has regular polygons as faces and has the same vertex configuration at all vertices but is not vertex-transitive: it is not true that for any two vertices, there exists a symmetry of the polyhedron mapping the first isometrically onto the second. Thus, although all the vertices of a pseudo-uniform polyhedron appear the same, it is not isogonal. They are called pseudo-uniform polyhedra due to their resemblance to some true uniform polyhedra.

Octadecahedron Polyhedron with 18 faces

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Gyroelongated cupola

In geometry, the gyroelongated cupolae are an infinite set of polyhedra, constructed by adjoining an n-gonal cupola to an 2n-gonal antiprism.

Chamfer (geometry)

In geometry, chamfering or edge-truncation is a topological operator that modifies one polyhedron into another. It is similar to expansion, moving faces apart and outward, but also maintains the original vertices. For polyhedra, this operation adds a new hexagonal face in place of each original edge.

Icosahedron Polyhedron with 20 faces

In geometry, an icosahedron is a polyhedron with 20 faces. The name comes from Ancient Greek εἴκοσι (eíkosi) 'twenty' and from Ancient Greek ἕδρα (hédra) ' seat'. The plural can be either "icosahedra" or "icosahedrons".

Elongated gyrobifastigium Space-filling polyhedron with 8 faces

In geometry, the elongated gyrobifastigium or gabled rhombohedron is a space-filling octahedron with 4 rectangles and 4 right-angled pentagonal faces.

References