I'm having trouble figuring out how to create admissible heuristics from cost functions.  For example, if I was trying to create an admissible heuristic from a cost function that takes in starting position and ending position and returns the cost based on differences in height, I don't understand how to create an admissible heuristic from such a basic function.Any help would be greatly appreciated.
Creating admissible heuristics from functions?
algorithms;heuristics