Cyclides and the guiding circle

Using the fact that spheres of 3D correspond to points in 4-dimensional space which lie outside a certain quadric, we introduce a new shape handle that permits the control of general cyclides: the guiding circle. A general cyclide is the envelope of a quadratic family of spheres which in this context is a conic in 4-dimensional space. The guiding circle is associated to the cyclide via the plane of the conic that corresponds to the cyclide.