The Square Antiprism
The square antiprism is a 3D uniform polyhedron bounded by 2 squares and 8 triangles. It has 16 edges and 8 vertices.
The height of a square antiprism with an edge length of 2 is 23/4, or approximately 1.68179.
A square antiprism can be capped with a square pyramid to form the gyroelongated square pyramid (J10), a Johnson solid, or with two square pyramids to form the gyroelongated square bipyramid (J17), another Johnson solid.
In order to be able to identify the square antiprism in various projections of 4D objects, it is useful to know how it appears from various viewpoints. The following are some of the commonly-encountered views:
Parallel projection centered on square face.
Parallel projection parallel to square faces and a pair of triangles.
Vertex-centered parallel projection.
Parallel projection centered on an edge between two triangles.
The Cartesian coordinates of the square antiprism, centered on the origin and having edge length 2, are:
- (0, ±√2, 1/∜2)
- (±√2, 0, 1/∜2)
- (±1, ±1, −1/∜2)