A method for determining the physical location of a vehicle being guided with an onboard navigational positioning system capable of detecting and generating a positioning location vector for the vehicle. The method includes the steps of detecting and receiving a plurality of electromagnetic radiation signals. A plurality of ambient parameter measurements is also received. A confirming location position is calculated from the plurality of electromagnetic radiation signals and the plurality of ambient parameter measurements. The confirming location position is compared to the positioning location vector generated by the onboard system to create a differential vector. If the confirmation location position and the positioning location vector are greater than a predetermined value, the positioning location vector generated by the onboard navigational positioning system is prevented from being used in directing the movement of the vehicle until the position differential is below a predetermined error value.