Approximation of the Distance from a Point to an Algebraic Manifold

The problem of geometric distance d evaluation from a point X0 to an algebraic curve in R2 or manifold G(X) = 0 in R3 is treated in the form of comparison of exact value with two its successive approximations d(1) and d(2). The geometric distance is evaluated from the univariate distance equation possessing the zero set coinciding with that of critical values of the function d2(X0), while d(1)(X0) and d(2)(X0) are obtained via expansion of d2(X0) into the power series of the algebraic distance G(X0). We estimate the quality of approximation comparing the relative positions of the level sets of d(X), d(1)(X) and d(2)(X).