Superellipsoid


In mathematics, a superellipsoid or super-ellipsoid is a solid whose horizontal sections are superellipses with the same exponent r, and whose vertical sections through the center are superellipses with the same exponent t.
Superellipsoids as computer graphics primitives were popularized by Alan H. Barr. However, while some superellipsoids are superquadrics, neither family is contained in the other.
Piet Hein's supereggs are special cases of superellipsoids.

Formulas

Basic shape

The basic superellipsoid is defined by the implicit inequality
The parameters r and t are positive real numbers that control the amount of flattening at the tips and at the equator. Note that the formula becomes a special case of the superquadric's equation if t = r.
Any "parallel of latitude" of the superellipsoid is a Lamé curve with exponent r, scaled by :
Any "meridian of longitude" is a Lamé curve with exponent t, stretched horizontally by a factor w that depends on the sectioning plane. Namely, if x = u cos θ and y = u sin θ, for a fixed θ, then
where
In particular, if r is 2, the horizontal cross-sections are circles, and the horizontal stretching w of the vertical sections is 1 for all planes. In that case, the superellipsoid is a solid of revolution, obtained by rotating the Lamé curve with exponent t around the vertical axis.
The basic shape above extends from −1 to +1 along each coordinate axis. The general superellipsoid is obtained by scaling the basic shape along each axis by factors A, B, C, the semi-diameters of the resulting solid. The implicit inequality is
Setting r = 2, t = 2.5, A = B = 3, C = 4 one obtains Piet Hein's superegg.
The general superellipsoid has a parametric representation in terms of surface parameters -π/2 < v < π/2, -π < u < π.
where the auxiliary functions are
and the sign function sgn is
The volume inside this surface can be expressed in terms of beta functions = ΓΓ / Γ, as: