An interpolation between a 'double sphere' and a torus [Une interpolation entre une 'double sphère' et un tore].

                    X = Fx(u,v)

                    Y = Fy(u,v)

                    Z = Fz(u,v)

                    u ∈ [Umin,Umax]

                    v ∈ [Vmin,Vmax]

                       v ^
                         |
                    V    |...... ---------------------------
                     max |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                         |      |+++++++++++++++++++++++++++|
                    V    |...... ---------------------------
                     min |      :                           :
                         |      :                           :
                         O------------------------------------------------->
                                U                           U              u
                                 min                         max

                    X = Mx(i,j)

                    Y = My(i,j)

                    Z = Mz(i,j)

                    i = f(u,Umin,Umax,Nu)

                    j = g(v,Vmin,Vmax,Nv)

• Fx
• Fy
• Fz