function Sphere(radius){
    Shape.call(this);

    /**
     * @property {Number} radius
     */
    this.radius = radius!==undefined ? Number(radius) : 1.0;
    this.type = Shape.types.SPHERE;

    if(this.radius < 0){
        throw new Error('The sphere radius cannot be negative.');
    }

    this.updateBoundingSphereRadius();
}
Spherical shape
@class Sphere
@constructor
@extends Shape
@param {Number} radius The radius of the sphere, a non-negative number.
@author schteppe / http://github.com/schteppe