Enhancing Mobile Robot Navigation in Urban Environments by a Polar Traversability Index

This paper presents a navigation method for a mobile robot in urban environments. The navigation method employs a socalled Polar Traversability Index (PTI) to evaluate terrain traversal property along a specific direction and guide the robot’s motion. In the navigation system, a 2-D Laser Rangefinder (LRF) is used to produce terrain maps in various formats, such as 3-D point-cloud map, 2.5 D elevation map and terrain traversability map. In order to generate a reliable elevation map for navigation, a filtering method based on the robot motion constraint and the LRF’s characteristics is used to filter out erroneous range data. The elevation map is converted into a one-dimensional PTI histogram where each PTI dictates the level of difficulty for the robot to traverse the terrain in the corresponding direction. The PTI histogram is then used to determine the robot’s motion commands⎯speed and steering rate. The PTI histogram enhances the robot’s navigational capability in urban environemts. For instances, it enables the robot to traverse wheelchair ramps and avoid curbs when negotiating sidewalks and it allows the robot to sanke through a ramp which may be too steep to travel for a robot using existing traversbility measures. The efficacy of PTI has been verified by simulation and experiments in a complete navigation system.