A sensor array which extends only over a fraction of the length of the vehicle generates pick-up signals in response to signals emitted by a ground wire lying in the ground. The pick-up signals are processed in signal-processing circuits to generate a heading signal and a displacement signal representing...http://www.google.com.tw/patents/US4310789?utm_source=gb-gplus-share專利 US4310789 - Vehicle which is steerable along a guide wire lying in the ground
