Congratulations - you have successfully made me look like an idiot! I've been staring at this with my head tilting from side to side, trying to work it out for the last 5 mins lol :-)
@elizabeth264 Tks Elizabeth..it's very easy..My camera, Nikon D90, has an overlay mode.. I took the first picture of the tracks then took the second one at 90 degrees and laid them on top of each other...works well