Photos as below show the route with a length of about 1.2 km that the robot has driven in both directions. In the meantime, the robot perform various field tests. Generally, the robot moved along a path surrounded by trees.
Another photo shows an enlarged section of this path. In the lower right corner of this photo I've marked the reference distance of 2m. In these tests, I've used the NEO-6M GPS module working with horizontal position accuracy 2.5 m (CEP 50%) . This accuracy depends on weather conditions and the number of visible satellites. Soon I'm going to test and compare other GPS modules so follow the entries in this log.