a controller is provided , operable to control a system on the basis of measurement data received from a plurality of sensors indicative of a state of the system , with at least partial autonomy , but in environments in which it is not possible to fully determine the state of the system on the basis of such sensor measurement data . the controller , comprises : a system model , defining at least a set of probabilities for the dynamical evolution of the system and corresponding measurement models for the plurality of sensors of the system ; a stochastic estimator operable to receive measurement data from the sensors and , with reference to the system model , to generate a plurality of samples each representative of the state of the system ; a rule set corresponding to the system model , defining , for each of a plurality of possible samples representing possible states of the system , information defining an action to be carried out in the system ; and an action selector , operable to receive an output of the stochastic estimator and to select , with reference to the rule set , information defining one or more corresponding actions to be performed in the system .