Error Analysis of Attitude Measurement in Robotic Ground Vehicle Position Determination

Abstract

: Position and attitude information from sensors employing carrier-phase differential GPS technology offer precise measurements that can be used for robotic ground vehicle control, notably in the automatic steering of farm tractors. The difference in location between the master GPS antenna on the vehicle's roof and the vehicle's control point requires that a lever-arm correction be added to the position measurement taken at the antenna to calculate the control point position. This lever-arm correction is a nonlinear function of noisy attitude and lever-arm measurements and introduces additional uncertainty into the position measurement at the control point. An approximation for the additional uncertainty is derived and verified through Monte Carlo simulations. Using realistic noise and lever-arm values for a medium-sized farm tractor, Gaussian attitude measurement noise above 0.4 deg (1 s) was shown to be the dominant source of position uncertainty at the control point when using carrier-phase differential GPS for centimeter-level position measurement. This analysis illustrates the importance of precise attitude measurements in minimizing the position measurement uncertainty at the vehicle's control point.