Hello All, I have a question about defining A* heuristic. I am trying to implement an algorithm in a paper using BGL. Here authors have used A* Dijkstra's to calculate shortest route with an additional constraint of route length should be no longer than a threshold value t. I think due to this threshold constraint they are using A* instead of normal Dijkstra's algorithm. I came to know A* is already there in Boost Graph Library. I just have a basic knowledge about A* algorithm that it finds the shortest route based on the heuristic H. I tried to look into the example in BGL, but I did not get any hint to define a heuristic. Can anybody give me some hints or some useful links of how can I define a heuristic for this particular scenario of finding the shortest path between nodes that is no longer than threshold t through A* Dijkstra. This would be really helpful for me to proceed further. -- Regards, Giridhar