I. Introduction
As unmanned ground vehicles (UGVs) will operate on increasingly varied and complex terrain, effective terrain traversability mapping becomes a critical factor for their safe navigation. LiDAR sensors have been widely deployed due to their advantages of high sensing accuracy and low lighting tolerance over visual sensors. Several methods have been proposed to convert LiDAR data into terrain data for traversability analysis, including point cloud [1], 3D grid [2], and 2.5D elevation mapping [3] methods.