Terrain Mapping

Perception research in the Planetary Rover project (Ambler walking robot) focuses on techniques to robustly perceive rugged terrain. The approach is to use a laser rangefinder sensor to construct terrain representations for tasks such as locomotion and navigation. A key contribution of this research is a perception system that does not depend on the controlled conditions of industrial settings, but functions in unstructured, outdoor environments.

Sensing: The primary sensor is a scanning laser rangefinder that directly measures range. A calibration procedure identifies the sensor position and orientation by observing the legs of the Ambler. Image preprocessing compensates for undesirable effects on the range measurements caused by temperature variations, ambient light, and material properties.

Map Construction: Planetary rovers use terrain maps for many tasks. For locomotion, the Ambler accesses elevation maps to select footfall locations and ensure collision-free leg and body trajectories.

Map Mosaics: Merging elevation maps from successive viewpoints allows the construction of a composite map. A two-stage algorithm has been developed to determine the correspondence between elevation maps constructed locally or from an overhead orbiter.

Long-Duration Operation: Typical scenarios for planetary missions involve traversing and partially mapping hundreds of kilometers. This requires the perception system to process massive amounts of data, and places a premium on efficient management of computing resources. The design of the mapping system minimizes the amount of data stored while maximizing the speed of map computation. Further, the mapping system monitors performance and resource usage statistics in order to quantify the computing requirements for a planetary mission.

Current Work: Research in progress seeks to develop two new capabilities: automatic map correction, and mapping terrain compliance. The approach for updating and correcting maps is to use position feedback from the Ambler legs to periodically refine the calibration parameters of the rangefinder. The method for mapping terrain compliance is to analyze the force/displacement profiles of each step, recording the results in a “material” map.