I was working a seismic site with a pretty tight resolution, I can't quite remember but I think it was 10m shots on 20m lines, with crossing lines every 100m, something like that. An older gent, who had grown up in the woods tried to cross from one line to the next, so not far, but when he got to the line, his crew were not where he thought they should be. The lines were mulcher cut, so pretty clear visibility along them. He was in radio contact with them, tried to cross back to his starting point, and then close in on his crew by the sound of their chainsaws. At this point no one has seen the guy for 45 minutes and we are about to send the helo for a search pass, he turns up on a line that has been tagged, so he can use that to pinpoint his location (the drilled holes are tagged and numbered) he was a line back behind his start point, and quite a distance from the crossing line where his crew was. But he was sure he hadn't crossed more than one line. 20 meters was all it took to get off course, and somehow either he hit a narrow spot in the cleared line, or the fresh show hid the mulch, not sure, but he was way off course. Navigating by the sun, and on a cut grid. he should have not been able to leave that wooded block, but somehow he ended up far off course.