[OSM-dev] Some help with proj.4
frederik at remote.org
Sun Apr 8 14:59:12 BST 2007
> 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