“…This approach contributes to enhancing the precision of the entire navigation system. When passing through a tunnel, although the signal is blocked and the information is inaccurate, the attitude information in the TMR digital compass is accurate and can continue to provide attitude correction for the [ 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ].…”