This class represents spheres.

A sphere is defined by its

• radius
• center
• northAxis
• refAxis

northAxis defines the direction from the center to the north pole. 

refAxis, a vector orthogonal to northAxis, the prime meridian. 

Latitude is defined by the U parameter, which defaults to [-OdaPI/2, OdaPI/2] for closed spheres. The lower bound maps to the south pole, zero maps to the equator, and the upper bound maps to the north pole. 

Longitude is defined by the V parameter, which defaults to [-OdaPI, OdaPI) for closed spheres. Zero corresponds to the meridian defined by the refAxis of this sphere. Applying the right hand rule along the northAxis defines the increasing direction for V. However, if isReverseV() is true, the increasing direction for V is defined by the left hand rule. 

The sphere is periodic in V with a period of Oda2PI. 

[umin, umax] by [vmin, vmax] defines a spherical patch with 4 sides bounded by 2 longitudinal arcs and 2 latitudinal arcs. 

The following constraints apply when defining a patch. 

• umin < umax and |umin - umax| <= OdaPI.
• vmin < vmax and |vmin - vmax| <= Oda2PI.

Corresponding C++ library: TD_Ge 

Working with Spheress