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Re: How to identify start node and end node in shortest_path_astar.....

by Nguyen Thi Van An :: Rate this Message:

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Hi Anton A. Patrushev,

Thanks for your help. But I it's not what I mean.

My problem here is drawing the shortest path on the map.

The user clicked on 2 points, but the shortest path begins and ends with 2 nodes. The shortest path between 2 nodes is ok. But it's a matter with the start path (the path contains start point) and the end path (the path contains end point) because the user don't click exactly the available coordinate on your roads. If both start path and end path are multilinestring which are not straight, how can you draw exactly that path from the user's start clicked point to his end clicked point?

Thanks,

Anton A. Patrushev wrote:

Hi Nguyen

You can use Distance function of PostGIS.
Here is an example:

SELECT Distance(geom_column, GeomFromText('POINT(x y)',
projection_code)) AS dist
FROM table_name
ORDER BY dist LIMIT 1";

where
geom_column - the name of the column which contains geometry;
'x y' - coordinates of your point divided by space;
projection_code - the code of projection you're using;
table_name - the name of the table.

It will search in entire table, so it will be nice to apply a filter to
the search, but anyway you'll have an idea.

Good luck!

Anton A. Patrushev
Software Engineer
Orkney, Inc.
6F JA-Kyosai Yokohama Building,
1-2 Kaigandori, Naka, Yokohama 231-0002 JAPAN
Tel 81-45-228-3320 Fax 81-45-228-3321
www.orkney.co.jp

> 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.
> _______________________________________________
> postgis-users mailing list
> postgis-users@postgis.refractions.net
> http://postgis.refractions.net/mailman/listinfo/postgis-users
>

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« Return to Thread: How to identify start node and end node in shortest_path_astar when the user click 2 points on the map?