Polypolar lemniscate coordinate system

The polypolar coordinate system, as well as classical polar, characterizes a point on a plane by polar radius $\rho$ and polar angle $\varphi$, but utilizes multiple poles instead of one pole. Such referencing can be provided by a class of multifocal lemniscates. The family of isometric curves $\rho=const$ — lemniscates — and family of gradient curves $\varphi=const$ are mutually orthogonal conjugate families.