[Cartoweb-users] Looking for single-destination (shortest path)program

zze-SIGALE PORTANERI F ext RD-BIZZ-SOP fportaneri.ext at rd.francetelecom.com
Fri May 12 03:13:12 EDT 2006

Hi Fay,
In fact, dijkstra is already calculating a graph from one point of the network (the source) to all other points. See http://www.nist.gov/dads/HTML/singleSourceShortestPath.html
An animation can be also found at http://www.cs.auckland.ac.nz/software/AlgAnim/dijkstra.html
The current pgdijkstra shortest_path() fonction launches the full graph calculation and then retrieve the stack of path only for the given target id.
It can be very simple (i.e. with one call to dijksta) to get the nearest car from the client by using the client as the source point. It needs some extension to the current dijkstra contrib code to pass one source id (client) and an array of target (cars) to the current shortest_path function: When the graph is complete, you just need to choose the target from the list which gives the smaller cost.
However, one problem could be that you have a directed network, and the shortest path from the client to the car could be different than the shortest path from the car to the client.... but may be it can help.


De : cartoweb-users-bounces at lists.maptools.org [mailto:cartoweb-users-bounces at lists.maptools.org] De la part de Fay Du
Envoyé : jeudi 11 mai 2006 21:58
À : cartoweb-users at lists.maptools.org; postgis-users at postgis.refractions.net
Objet : [Cartoweb-users] Looking for single-destination (shortest path)program

Hi everyone:
   I am trying to use pgDijkstra in my project. pgDijkstra calls boost library which provides single-source shortest function. My network is a street network. The graph is directed. My typical scenario is, there is one client calls dispatch center and there are many cars (for example, 100 cars) are available all over the network. I want to find the closet car and dispatch it to the client. It is a single-destination problem. Does anyone know if there is an existing single-destination program exists available for my project? Or the explanation of the single-destination algorithm?
   I know I can call pgDijkstra multiple times to get the answer. The performance of the solution is not good. Our goal is to calculate shortest paths of 100 cars to the same destination in less than a second. Calling pgDijkstra 100 times takes much, much more time than our goal.
Many, many thanks.
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