A sphere is represented by its location (center), axis, and radius. The axis
vector represents the axis around which the parameterization is 0 to 2pi and
is u. The reference direction vector indicates the orientation of the 0
parameter value in u. It need not be perpendicular to the axis vector but
must not be parallel to it. V parameterization is -pi/2 to +pi/2, on an
implicit generator of a half-circle. Looking at the sphere in the direction
opposite the axis vector, -p on the generator is away from the observer.
U increases counterclockwise, and v increases towards the observer.