Path planning for mobile robot on rough terrain based on sparse transition cost propagation in extended elevation maps

To efficiently evacuate an area threatened by volcanic disaster, onsite observation of active volcanoes by remotely controlled mobile robot systems is desired. Issues involved with developing such systems include planning a safe path for the robots. In this research, our objective was to realize a safe path planning method based on a digital elevation map (DEM) of volcanic mountain fields that considers the mobility of a mobile robot. We assumed that the DEM is obtained through airplane laser measurements beforehand. Because the target environment is vast, obtaining a DEM with sufficiently high resolution is difficult. Even if this is possible, path planning based on such a high-resolution DEM in vast environments significantly increases the computational load. Therefore, we propose a path planning method that can be applied to any DEM resolution; path planning is seamlessly performed roughly in a global scale and precisely in local scales. We extended the general DEM into 3-D space by adding an axis to denote the discrete heading direction of a mobile robot, which we call an extended elevation map (EEM). In the 3-D space EEM, the transition-cost from the start position is derived for each voxel by considering the mobility of the mobile robot. The transition-cost is sparsely propagated from the start position, and the sparsely valued field derives a single path with the lowest transition-cost to reach the goal position. The proposed method was implemented, and simulation experiments using DEMs of real volcanoes were performed to confirm its validity.