[postgis-users] How to identify start node and end node in shortest_path_astar when the user click 2 points on the map?

[Nguyen Thi Van An]

Hi everybody,

I'm  doing a project which needs to find a shortest path between two 
user's clicked points. I already  installed successfully  pgRouting.

I use this function:
SELECT * from shortest_path_astar('SELECT gid as id, source, target, 
length as cost, x1, y1, x2, y2 FROM roads', 3, 7, false, false);

But the problem is that I can't identify exactly the start node and end 
node to find path (How to identify node 3 and node 7?). I already have 
the start point and end point of the user. But they don't select 
correctly the points on my roads. So I can't draw the path correctly on 
the map (The path begins with their start clicked point and ends with 
their end clicked point)

Anybody has experiences with this? Please help me!

Thanks so much.