Global Navigation Satellite Systems (GNSS) and Inertial Navigation Systems (INS) play pivotal roles in modern navigation and positioning applications. The integration of these two technologies has become crucial for achieving high-accuracy and robust navigation solutions in various domains, such as autonomous vehicles, aviation and mobile devices. These two technologies are characterized by complementary features, with GNSS providing absolute position but suffering from dependency on external conditions and INS offering continuous, high-rate relative motion data but being affected by error accumulation over time. Their integration aims to emphasize strengths while minimizing weaknesses for robust and accurate navigation solutions. Several integration approaches, of different complexity, can be found in literature.