  A path from s to t on a polyhedral terrain is descending if the height of a
point p never increases while we move p along the path from s to t. No
efficient algorithm is known to find a shortest descending path (SDP) from s to
t in a polyhedral terrain. We give two approximation algorithms (more
precisely, FPTASs) that solve the SDP problem on general terrains. Both
algorithms are simple, robust and easy to implement.
