ABSTRACTA closed‐form solution of the GPS pseudorange equations, an unaided Kalman filter, and an inertially‐aided Kalman filter are used with differential GPS postprocessing to produce reference trajectories for evaluation of GPS user‐equipment, for evaluation of integrated host vehicle navigation, and for accurate Time Space Position Information over large operating areas.The closed‐form solution was developed in a derivation of existence conditions for solutions to GPS pseudorange equations. The derivation is included here as an Appendix. Positions calculated from the closed‐form solution are used for starting and monitoring the Kalman filters, and for responding to uploads and constellation changes. Custom interface modules adapt common core modules of the aided Kalman filter to various inertial n