1. A state estimation system for determining possible values of a measured data item comprising: a computer; at least one measurement input to the computer measuring the data item, said measurement corrupted by noise; a computer output device; at least one restriction on the measured data item, said restriction available in memory to the computer; and a software module operating on the computer for calculating at least one estimate of the state of the measured data item based upon the measurement input and the restriction, and sending the estimate to the output device; wherein the software module calculates the estimate by: representing the state space of the measured data item as a finite set of points using the restriction; and applying a decision rule, said decision rule based on the finite set of points, to the measurement input.