A portable navigation module and its method of operation are disclosed for seamlessly providing navigation and positioning information to a user. The module comprises: means, such as a GPS receiver, for receiving a first set of navigational information from an external source, such as satellites; and an inertial sensor unit for generating a second set of navigational information at the module. The navigational information is used by a processor programmed with a core algorithm, to identify the mode of conveyance algorithm and an orientation or misalignment algorithm. The algorithm utilizes the navigational information, aided by the mode of conveyance information and the orientation information, to produce a filtered navigation solution (which comprises position, velocity and attitude). The solution is suitably displayed, preferably on a detachable display unit.The system has the following attributes: the solution is produced seamlessly, even if one source of navigational information is temporarily out of service; the accuracy of the solution is assisted by use of the mode of conveyance and orientation information; and there is no requirement for the module to be permanently aligned with the direction of movement of the conveyance platform.