There are 3 repositories under gps-ins topic.
Fusing GPS, IMU and Encoder sensors for accurate state estimation.
C++ Library for INS-GPS Extended-Kalman-Filter (Error State Version)
Qt/C++ GUI to Visualize Kitti Dataset GPS+IMU data on OpenStreetMap using EKF
Implementation of an EKF to predict states of a 6 DOF drone using GPS-INS fusion. Also ass3_q2 and ass_q3_kf show the difference between state estimation without KF and with KF