Range-domain integration of GPS and laser-scanner measurements for outdoor navigation

In this paper, an innovative navigation algorithm combining GPS and laser-scanner measurements is analyzed and tested in natural outdoor environments. Using carrier phase differential GPS, centimeter-level positioning of autonomous ground vehicles is achievable. However, GPS signals are easily attenuated or blocked, so their use is generally restricted to open-sky areas. In response, in this work we augment GPS with two-dimensional laser-scanner measurements. The two sensors are integrated in the range domain for optimal navigation performance. The GPS/Laser range-domain integration is performed using a measurement-differencing extended Kalman filter. In addition, the use of laser measurements requires that we address the feature extraction process, which aims at selecting features in the environment that can be consistently identified, and the data association procedure, which establishes correspondences between these extracted measurements and a continuously updated map of landmarks. Using this algorithm, the vehicle's position is determined throughout GPS outages, without a-priori knowledge of the surrounding landmarks' locations. Experimental testing in actual urban canyons in Chicago, where fewer than four GPS satellite signals are available, demonstrates, that the performance of the range-domain integrated positioning and mapping algorithm exceeds that of a more traditional position-domain implementation.