[OSM-dev] Some help with proj.4

Frederik Ramm frederik at remote.org
Sun Apr 8 14:59:12 BST 2007

Hi Stefan,

> For the search we query this data and take an heuristic approach. And
> query SQLite in a smart way.
> SELECT * FROM junctions WHERE (start = $myfrom AND end = $myto) OR
> (start = $myfrom AND end = $myto AND direction=2);
> Where you get back the next junctions to take.

I don't want to be rude here but the words "dream on" have just crossed 
my mind ;-)

Maybe I, in turn, see too many difficulties where there are none, but I 
do not believe that simply applying a standard path finding algorithm 
will do the trick, at least not on usual hardware, because of the sheer 
size of the graph. Of course, on a very theoretical level, any 
run-off-the-mill algorithm (must admit ignorance concerning A*, have 
always used Dijkstra's, will read up on it) *will* find the shortest and 
fastest way between any two nodes, and yes you're right, I said that I'd 
be happy to get any result at all but even I didn't want to wait three 
hours for my route from Hamburg to Munich.

In this case, optimizations make the difference between a practical 
algorithm and an unusable one. I could try to replace start and 
destination by their nearest motorway connection and route between these 
on the motorway-only network - but good routing solutions will also give 
you a route from Hamburg to Munich if you say "avoid all motorways". So 
there's definitely a lot of problem solving (and reading up on what 
others are doing) invovled.


Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'

More information about the dev mailing list