[pgrouting-users] Different comportment between 'shortest_path_astar' and 'driving_distance' functions.

[Schembri Samuel]

Hi Steve,

This is zip file with:

*Bug1.png You can see :

 - Shortest_path function result : Green line
 - Graph with digitalisation sens
 - Id of vertex
 - One way of 2 edges : red arrows

To go to vertex(48) since vertex (540), pgrouting is doing good choice because  the edge (2: gid 51) has a big cost value . Full distance is 1159 meters.

*Bug2.png You can see :

 - Driving distance result: blue labels and variant color : Distance ( meters)
 - Edges used by pgrouting : blue line
 - One way of 2 edges : red arrows

To go to vertex(48) since vertex(540), pgrouting takes the edge (2) with big cost value and he used reverse_cost  value to calculate full distance.

Distance vertex must be egal to  1159.


*Dump with my graphe . (create a tif1104 schema before import)

Query:


 select * 
 from shortest_path('
     select 
      id
      ,source
      ,target
      ,cost
      ,reverse_cost,
      to_cost
      ,rule
       
     from  
      tif1104.graphe
     where 
      statut is true
      order by id',
     540,
    48,
    false,
    true )

select 
* 
from  
 driving_distance(' 
    select 
     id
     ,source
     ,target
     ,cost
     ,reverse_cost
     ,to_cost
     ,rule
    from 
     tif1104.graphe
    where 
     statut is true
    order by id',
    540,
    2000,
    false,
    true)
 
Best regards ...
 
Samuel
 

 


-----Message d'origine-----
De : pgrouting-users-bounces at lists.osgeo.org [mailto:pgrouting-users-bounces at lists.osgeo.org] De la part de Stephen Woodbridge
Envoyé : lundi 16 janvier 2012 17:22
À : pgrouting-users at lists.osgeo.org
Objet : Re: [pgrouting-users] Different comportment between 'shortest_path_astar' and 'driving_distance' functions.

On 1/16/2012 9:36 AM, Schembri Samuel wrote:
> Hi steve,
>
> Thank you for the response.
>
> Why I would like to used this method. I prefer driving-distance 
> functions because when we must compute a lot of distances with same 
> departure point, this method is more fast than 'shortest_path_astar'
> method. After, I can get distance with nodes directly.
>
> Example : get distance between shop and 100 customers.

Yes, this makes sense. I wrote some code a while ago that does some similar using driving distance code, but I did not check if the reverse cost were working.

> I can create little graphe ,function, and snapshot.
>
> How would you like receive these informations ?

If you want to generate a SQL dump of the above that would be great. If the results are simple enough to generate an expected results table so we can compare the actual results against the expected results that would be great, but if it is too complax than we can figure it out later.

Thanks,
   -Steve

> Regards
>
> Samuel
>
>
>
>
>
>
> -----Message d'origine----- De :
> pgrouting-users-bounces at lists.osgeo.org
> [mailto:pgrouting-users-bounces at lists.osgeo.org] De la part de Stephen 
> Woodbridge Envoyé : lundi 16 janvier 2012 15:14 À :
> pgrouting-users at lists.osgeo.org Objet : Re: [pgrouting-users] 
> Different comportment between 'shortest_path_astar' and 
> 'driving_distance' functions.
>
> Hi Samuel,
>
> I'm not sure I can answer your question with doing some additional 
> research of reading through the code, but the driving directions does 
> not get much use and it is possible that it has a bug that noone has 
> reported until now.
>
> Your example seems like a really good test case. I am trying to 
> collect simple and clear test cases so we can develop a test suite 
> that can be run before we release code to validate changes in a 
> release have not broken anything. If you could create a ticket and 
> attach your test cases or just send them to me off list, I can create 
> a ticket for them.
>
> -Thanks, -Steve
>
>
>
> On 1/16/2012 3:14 AM, Schembri Samuel wrote:
>> Hi, I am new user of this pgrouting users list. I hope used 
>> correctly. I used pgrouting 1.02 on postgres 8.2.17. At this time, I 
>> can't update Postgresql. There is a different comportment between 
>> 'shortest_path_astar' and 'driving_distance' functions when I use 
>> reverse_cost column. Here are graphe conditions :
>>
>> * For each edge without one-way : cost=reverse_cost=length * For each 
>> edge with one-way similar to digitalisation way : cost=length
>> reverse_cost=-1 (or 100000) * For each edge with one-way inverse of 
>> digitalisation way : cost=-1 (or 100000) reverse_cost=length * All 
>> another edges are not in graphe.
>>
>> *shortest_path_astar:* /has_reverse_cost = false : / Edges with 
>> 'cost=-1' are forbiden and Pgrouting don't used them.
>> 'Reverse_cost' information is not used. /has_reverse_cost = true:/ 
>> Edges with 'cost=-1' are used if 'reserve_cost' is more than 0.
>> Cost used by pgrouting is 'reserve_cost' column. Edges with 
>> 'reverse_cost=-1' are used if 'cost' is more than 0. Cost used by 
>> pgrouting is 'cost' column. T his computing is correct.
>> *Driving_distance:* ** /has_reverse_cost = false : / Edges with 
>> 'cost=-1' are forbiden and Pgrouting don't used them.
>> 'Reverse_cost' information is not used. /has_reverse_cost = true:/ 
>> /Case one : Edge with 'cost=-1' and 'reverse_cost=length':/ Edge can 
>> be traveled on digitalisation way ( cost =-1!!). Cost used by 
>> pgrouting is 'Reverse_cost' column. /Case two : Edge with cost=length 
>> and reverse_cost=-1:/ Edge can be traveled on inverse digitalisation 
>> way. More, Cost used by pgrouting is 'cost' column.
>> In this two case, pgrouting don't respect restrictions. This 
>> computing is not correct. Could you me if this result is normal or 
>> not ? Sorry for my bad english and best regards Samuel -- Paris //
>>
>>
>> _______________________________________________ Pgrouting-users 
>> mailing list Pgrouting-users at lists.osgeo.org 
>> http://lists.osgeo.org/mailman/listinfo/pgrouting-users
>
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