$$x^2+y^2+z^2-\sqrt{3}=0$$

$$\Bigl(R-\sqrt{x^2+y^2}\Bigr)^2+z^2-r^2=0$$

$$\sin(z)-\sinh(x)\sinh(y)=0$$

$$x=\sin(t),\quad y=\cos(t),\quad z=0.1t$$

$$f(x,y)=\frac{\sin(r)}{r},\quad r=\sqrt{x^2+y^2}$$

Points aléatoires

$$\begin{aligned}x(u,v)&=\frac{2\cos(u)(\cos(u)\cos(2v)+\sqrt{2}\sin(u)\cos(v))}{3\Bigl(\sqrt{2}-\sin(2u)\sin(3v)\Bigr)}\\y(u,v)&=\frac{2\cos(u)(\cos(u)\sin(2v)-\sqrt{2}\sin(u)\sin(v))}{3\Bigl(\sqrt{2}-\sin(2u)\sin(3v)\Bigr)}\\z(u,v)&=-\frac{\sqrt{2}\cos^2(u)}{\sqrt{2}-\sin(2u)\sin(3v)}\end{aligned}$$