[pgrouting-users] dijkstra_sp result order

[Stephen Woodbridge]

Hi Julien,

Welcome to the community.

Julien-Samuel Lacroix wrote:
> Hi,
> 
> I'm trying to use the wrapper functions dijkstra_sp and astar_sp to find 
> the shortest path between to points. However the order of the output 
> seems to be wrong.
> The following:
> 
>    SELECT * FROM astar_sp( 'fcmqrouting19', 80, 3667)

Try:

    SELECT id, gid, astext(the_geom)
      FROM astar_sp( 'fcmqrouting19', 80, 3667);

Since the results are edges you need to check if the edge needs to be 
ordered from-to or to-from. So to order the edges you need to do 
something like this pseudo-code:

Loop through edges in results
   if first edge then
     if edge.start == next.start or edge.start == next.end then
       edge = edge.reverse  // now the first edge is in the correct order
     end
   else
     if last.end == edge.end then
       edge = edge.reverse
     end
   end
   last = edge
end loop

I have not seen the problem you mention below.

-Steve Woodbridge

> returns an un-ordered list of feature (The first line segment in my path 
> come in third place in the result set for example):
> 
> id; gid; the_geom
> 1;  617; "010...4640"
> 2;  513; "010...640"
> 3;  121; "010...4640"
> 4;  618; "0102...640"
> 5;  2;   "01020...40"
> 6;  4581;"0102...640"
> 
> If I use shortest_path (both astar or dijkstra) functions the order of 
> gid returned is:
> 121, 513, 617, 2, 618, 4581
> 
> My questions are:
> Is this a known bug?
> Is there a way to keep the order of my results and still have the "id" 
> column containing the row number (from 1 to 6 in my example)?
> 
> Best regards,
> Julien
>