I have 2 part question:
So I am new to the ALT algorithm and I have read a few papers on it to understand it a bit better.
What I really want to understand is what really is how is the Landmark weight different from the Astar weights?
After digging through the code I can see that one uses the beeline and the other uses landmark. But after some further digging, at some point, don’t both these values converge or similar to one other(I am sure they don’t, but I am not able to quite understand this) ?
That is → if the landmark weight is really an approximation of the distance from the node to the target node, shouldn’t it always be smaller than the A* beeline approx weight (which might be more accurate?) ? And hence, at the best case scenario shouldn’t Landmark be as good as A*, as the weights are essentially the same in the best case for each ?
I am sure they are the same as the performance clearly says otherwise, so I would love to understand this!
So I loaded up Norcal osm, and I ran a bidirectional A* algorithm, using Landmark routing factory, for a specific route and I looked into the weights. Now when I wrote my own implementation of A* and used the landmark approximator, for the same node and the same target node I got different weights… And the weights were similar to the ones that I get with the beeline approximator.
It would be great if anyone could help me with these 2 questions! Thank you!