  Reconstruction of the curvatures of radio wavefronts of air showers initiated
by ultra high energy cosmic rays is discussed based on minimization algorithms
commonly used. We emphasize the importance of the convergence process induced
by the minimization of a non-linear least squares function that affects the
results in terms of degeneration of the solutions and bias. We derive a simple
method to obtain a satisfactory estimate of the location of the main point of
emission source, which mitigates the problems previously encountered.
