Multi-Range Traversability Indices for Terrain-Based Navigation

1 Introduction This paper presents novel measures of terrain traversability at three different ranges; namely Local , Regional, and Global Traversability Indices. The Local Traversability Index is related by a set of linguistic rules to local obstacles and surface softness within a local perception range, measured by on-board sensors mounted on the robot. The rule-based Regional Traversability Index is computed from the terrain roughness and slope that are extracted from video images of the terrain within a regional perception range obtained by on-board cameras. The Global Traversability Index is obtained from the terrain topographic map, and is based on the natural or man-made surface features such as mountains and craters within a global perception range. Each traversability index is represented by four fuzzy sets with the linguistic labels (P O O R , LOW, MODERATE , HIGH), corresponding to surfaces that are unsafe , moderately-unsafe, moderately-safe, or safe f o r traversal, respectively. These indices are used to develop a behavior-based navigation strategy for a mobile robot traversing a challenging terrain. The traversability indices form the basis of three navigation behaviors; namely, Traverse-Local, Traverse-Regional, and Traverse-Global behaviors. These behaviors are integrated with the Seek-Goal behavior to ensure that the mobile robot reaches the goal safely while avoiding obstacles and impassable terrain segments. The paper is concluded b y an illustrative graphical simulation study '. Exploration of planetary surfaces and operation in rough terrestrial terrain have been strong motivations for research in autonomous navigation of field mobile robots in recent years. These robots must cope with two fundamental problems. The first problem is to acquire and analyze the terrain quality information on-line and in real time, and to utilize it in conjunction with limited prior terrain maps. The second problem is to deal with imprecision in sensor measurements and uncertainty in data interpretation inherent in sensing and perception of natural environments. With respect to these two fundamental problems, outdoor robot navigation defines a research topic that is more challenging than indoor robot navigation in structured and benign man-made environments. Robust on-line terrain characterization and traversability assessment are clearly core research problems for autonomous field robot navigation. Two types of solutions have been proposed by researchers at CMU and JPL. In the CMU methods [l-41, the terrain traversability is computed along different candidate paths that correspond to different robot steering angles. The traversability of each path is determined mathematically by a weighted …