An adaptive NHC-assisted GNSS/INS integrated positioning method

Accurate positioning is essential for train operational efficiency and automation. Although GNSS/INS/Non-Holonomic Constraints (NHC) integration provides continuous navigation, enforcing NHC during train side-slip, vibration, or track irregularities introduces significant positioning errors. To resolve this, we propose an adaptive NHC-assisted GNSS/INS integrated positioning method. First, an EKF tightly couples GNSS and INS measurements. Crucially, we design an NHC validity detector that constructs a test statistic from NHC observation residuals. This statistic is continuously compared against a detection threshold: NHC constraints are selectively activated only when residuals indicate validity; otherwise, they are automatically disabled to prevent error contamination. Field tests on railway lines demonstrate that the adaptive strategy: reduces lateral positioning RMS error by 11.4% compared to forced-NHC approaches.