Pgrouting - Networking

Question

my problem is regarding routing. I have a network based on bicycle graph links (SRID: 4326), with bidirected and directed ways. I want to give the user the functionality to draw a route (shortest path) from a given point to a certain location (the input parameters are sent from my app, as two geometric POINTS).

So to approach this problem i did the following steps:

1. Added reverse cost column and assigned an arbitrary high value for the ONE WAY links (Geometry LINESTRING)
2. Used the ST_ClosestPoint function to get the nearest source node from the start position, and the nearest target node from the final destination.

3. Once i have my source node and target_node i launched the Dijkstra Shortest Path function of pgrouting (taking account the reverse_cost for ONE WAY links):

   SELECT bz_bike_graph_line.* FROM bz_bike_graph_line JOIN 
       (SELECT * FROM shortest_path('SELECT gid as id, start_node::int4 as          
                        source, end_node::int4 as target, distance::double 
                        precision AS cost, reverse_cost::double precision 
                        AS reverse_cost FROM bz_bike_graph_line' ,source_node, 
                        target_node, true, true)) AS route 
        ON bz_bike_graph_line.gid = route.edge_id
   

QUESTION:

All seems to be working in the right way BUT when returning the route the starting point and the starting route node never coincides (idem target and final dest.), obviously i should say, due the fact we return the closest points. Is there a way to resolve it or solve the task in other way? Some GIS expert here :) ?

P.A. Thanks!

Answer 1

I believe this is more a problem of user interaction than GIS. IMHO I would:

1. warn the user if the desired start/end point is further away from the nearest point on the graph of, say 30m and offer her a choice to move them or keep them where they are

2. for distances less than 30m perhaps you could simply move the desired start/end point to the nearest point without warning or choice, but I wouldn't recommend it