RTK-LIO: Tightly Coupled RTK/LiDAR/Inertial Navigation System Based on Optimization Approach

Global Navigation Satellite System Real-Time Kinematic (GNSS-RTK) serves as a vital tool for providing absolute positioning for autonomous systems. However, its performance suffers considerable degradation in urban canyon environments due to the well-known challenges caused by multipath effects and Non-Line-of-Sight (NLOS). Light Detection and Ranging (LiDAR)/Inertial Odometry (LIO) offers high-precision local pose estimation in structured urban settings, but it tends to accumulate drift over time. Recognizing their complementary strengths, this paper proposes an adaptive integration of GNSS-RTK with LIO to achieve continuous and precise global positioning for autonomous systems in urban environments. The raw data is modeled and optimized within the framework of a factor graph. At the same time, double difference carrier phase and ambiguity are added to the estimated states. Finally, RTK-LIO is evaluated on public datasets. It greatly exceeds the benchmarks (LIGO, GLIO and RTK) in both accuracy and smoothness. To benefit the community, the implementation is open-sourced at https://gitee.com/bryantaoli/rtk-lio.