[dmcclurg]

The complexity of this problem is absurd. If the biker precisely know the terrain then he is capable of knowing where he is in that terrain. This is the basis of terrain-association.

[dmcclurg]

A hiker, I mean. The distinction is not important.

[rini17]

They can't see the terrain because of the trees.

Sure, in nature there are always some clues, but then it's more orienteering than geometry problem.

[caf]

Consider it a "lost in an ocean" problem instead then.