  Localization can be achieved by different sensors and techniques such as a
global positioning system (GPS), wifi, ultrasonic sensors, and cameras. In this
paper, we focus on the laser-based localization method for unmanned aerial
vehicle (UAV) applications in a GPS denied environment such as a deep tunnel
system. Other than a low-cost 2D LiDAR for the planar axes, a single axis Lidar
for the vertical axis as well as an inertial measurement unit (IMU) device is
used to increase the reliability and accuracy of the localization performance.
We present a comparative analysis of the three selected laser-based
simultaneous localization and mapping(SLAM) approaches:(i) Hector SLAM; (ii)
Gmapping; and(iii) Cartographer. These algorithms have been implemented and
tested through real-world experiments. The results are compared with the ground
truth data and the experiments are available at https://youtu.be/kQc3mJjw_mw.
