Device and method to estimate the state of a moving vehicle overflying a certain terrain. The device comprises a camera oriented toward the terrain, an inertial measurement unit, a device for the processing of images and a “navigation filter”. This filter uses an innovative method to obtain state estimates of the vehicle. Unlike the conventional art, only robust and flexible expressions are used here, producing accurate state estimates, with no possibility of divergence, with no need for initial state estimates or high computational power. The method calculates parameters describing geometrical relationships among points of the trajectory and others on the terrain. These parameters are combined with estimates of the accelerations to obtain estimates of the velocity at a given time and of the gravity acceleration vector. By integrating these estimates, velocity and position profiles are obtained. The state is expressed in a reference system fixed with respect to the terrain.