A modular device, system and associated method, used to enhance the quality and output speed of any generic GPS engine is provided. The modular device comprises an inertial subsystem based on a solid state gyroscope having a plurality of accelerometers and a plurality of angular rate sensors designed to measure linear acceleration and rotation rates around a plurality of axes. The modular inertial device may be placed in the data stream between a standard GPS receiver and a guidance device to enhance the accuracy and increase the frequency of positional solutions. Thus, the modular inertial device accepts standard GPS NMEA input messages from the source GPS receiver, corrects and enhances the GPS data using computed internal roll and pitch information, and produces an improved, more accurate, NMEA format GPS output at preferably 2 times the positional solution rate using GPS alone. The positional solution frequency using the present invention may increase to as much as 5 times that obtained using GPS alone. Moreover, the modular inertial device may assist when the GPS signal is lost for various reasons. If used without GPS, the modular inertial device may be used to define, and adjust, a vehicle's orientation on a relative basis. The modular inertial device and architecturally partitioned system incorporated into an existing GPS system may be applied to navigation generally, including high-precision land-based vehicle positioning, aerial photography, crop dusting, and sonar depth mapping to name a few applications.