[pgrouting-users] Optimize routing - use new sew-devel-2_0 functions

[Tao Romera Martinez]

Frederic,

The time to generate a route is mostly spent in retrieving the ways
from the DB and passing them to the C function that performs the
Dikstra, as Stephen once pointed out in a private mail to me. With a
small graph, 80% of the time consumed by shortest_path goes to
retrieving the ways.
If you really need to improve the efficiency of 1 search in your
service, you could consider modifying the C code to reuse the ways
retrieved from the DB and generate a new route with different
parameters.

Tao

2013/5/22 Daniel Kastl <daniel at georepublic.de>:
>
>
>
> On Wed, May 22, 2013 at 6:42 PM, Frédéric Bonifas
> <fredericbonifas at gmail.com> wrote:
>>
>> I agree the the routes will be relatively short for pedestrian routing,
>> but :
>> * if I understand correctly how Dijkstra works, the routing time will
>> mostly depend on the size of the graph, as the whole graph will be
>> visited before giving the shortest_route.
>> * the fastest it is, the more I like it :)
>> * I show to the user different possible routes (4) so the routing time
>> is multiplied by this factor.
>>
>
> Hi Frederic,
>
> The algorithm doesn't make such  big difference as you might expect.
> What matters is the size of the network that you load for a routing request,
> which depends on the length of the route and the road density.
> For example a 40km route through Tokyo will load a huge amount of data, but
> some sparse area in Canada 40km would not be an issue.
>
> For your pedestrian routing, did you make sure that you don't load the whole
> network table for every request?
> The easiest way to limit the data you select is using a BBOX.
>
>  Daniel
>
>
>
> --
> Georepublic UG & Georepublic Japan
> eMail: daniel.kastl at georepublic.de
> Web: http://georepublic.de
>
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-- 
Tao Romera Martínez

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