[pgrouting-users] Shortest Route Search Not Working

[Dan Putler]

Hi Daniel,

To follow on Yasir's comments in terms of routing results, I've been working with a simple example data set where the distance and travel time results are likely to be different (really there are several equally good routes based on distance, but a unique route based on travel time, but with the "length" field in the database reflecting travel time along an edge). When doing the routing based on travel time I get the correct solution using the Dijkstra algorithm, but an incorrect result using the A* and Shooting Star algorithms. The nature of the errors I'm getting would be consistent with what Yasir is finding. I'd be glad to send you both the network data and my test queries. I'm running on 64bit Ubuntu 10.04 using the Ubuntu repository version of PostgreSQL (8.4.4), PostGIS 1.5.1, and built pgRouting from the subversion repository on Tuesday.

Dan

--- On Fri, 7/16/10, Daniel Kastl <daniel.kastl at georepublic.de> wrote:

From: Daniel Kastl <daniel.kastl at georepublic.de>
Subject: Re: [pgrouting-users] Shortest Route Search Not Working
To: pgrouting-users at lists.osgeo.org
Received: Friday, July 16, 2010, 9:58 PM

 I hope you don't mind helping me with another couple short questions:
1. Projection 4326 with latlng is lot easier for me to work with. Although there are ways to convert the latlng to
 900913 projection, I was wondering how would I be able to directly use 4326 and run search on it (HTML changes), assuming that the tiles were generated with 900913 projection and the routing database is set to 4326?



You can use Postgis "transform()" function to do this: http://postgis.refractions.net/docs/ST_Transform.html

 

2. Just out of curiosity.
The routing results usually take residential route ways, instead of taking instead of taking highway streets (which is more like what results from Google Maps show). Any ideas why the difference?



pgRouting gives you the "shortest" path and it's up to you to define what is "shortest". Easiest is to take length as cost, but if you take time as cost, then shortest will be the fastest. You could for example define some speed for your road classes, and if the speed is higher on highways it will prefer the highway like Google Maps does.


Daniel
 

Thanks


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