/// <summary>
/// Create a new Object3D, place it on the stage, add to Model3D's instance collection,
/// and if collidable add to collision collection.
/// </summary>
/// <param name="position"> location of new Object3D</param>
/// <param name="orientAxis"> axis of rotation</param>
/// <param name="radians"> rotation on orientAxis</param>
/// <returns> the new Object3D</returns>
public Object3D addObject(Vector3 position, Vector3 orientAxis, float radians)
{
Object3D obj3d = new Object3D(stage, this, String.Format("{0}.{1}", name, instance.Count),
position, orientAxis, radians, Vector3.One);
obj3d.updateBoundingSphere(); // need to do only once for Model3D
instance.Add(obj3d);
if (IsCollidable) stage.Collidable.Add(obj3d);
return obj3d;
}
