The polymorphic estimator algorithm proposed by the first author, \textit{R. Vojak} and \textit{R. G. Hutchins} [J. Guid. Control Dyn. 16, 865-873 (1993)] is modified in order to improve the tracking performance in the presence of discontinuities. The novelty of the approach results from the measurement architectures. This algorithm is shown by example to be superior to both an extended Kalman filter and the earlier polymorphic estimator.