[OSRM-talk] OSRM-talk Digest, Vol 27, Issue 12
Francis
francisrute at gmail.com
Thu Apr 9 16:28:49 UTC 2015
Hi Romain,
I would also be pretty interested in a bicriteria (or multicriteria) OSRM
version. What bicriteria algorithm would you like to use?
Let me first introduce myself. I'm involved in a SmartCities European
Project in my city and we would like to provide routes that consider the
minimization of multiple criteria simultaneously, like travel time,
economic cost or CO2 emissions. I'm about to finish my phD in
Multiobjective Shortest Path Problems and I'd love to apply some of the
algorithms I have developed to that project. I do believe OSRM may be a
great starting point for such a service.
I have started recently to inspect the source code. Let me point out some
of the issues concerning an OSRM service that minimizes simultaneously more
than one criterion:
- Multiple lua profiles could be necessary (one for each criterion).
- Edge weights are no longer a scalar value, but a vector of n dimensions
(n- number of criteria).
- The preprocessing of the input graph and the routing algorithm
(Contraction Hierarchies and bidirectional Dijkstra) must be adapted to the
Multicriteria case, specifically, the preprocessing process were shortcuts
are added as well as the search process were bidirectional Dijkstra's
algorithm is employed to find the shortest path.
- Since the concept of optimum does not apply to Bicriteria or
Multicriteria search, the new multiobjective algorithm would return a set
of solutions, typically the set of Pareto or non-dominated solutions.
- Unless the two considered criteria are highly correlated (like travel
time and distance, for example), the number of Pareto solutions is usually
big (hundreds, thounsands...), so in order to make it practical for the
user to choose one of the alternatives, something else from Multicriteria
Decision Making would be necessary (Goal Programming, Compromise Search,
tighten the concept of dominance...).
- The frontend receives and paints several routes.
I'm not sure how this would be interesting for the rest of the community,
but I'd like to show an example of why this could be pretty useful.
Let me assume we are considering two criteria, travel time and the economic
cost of the route (gas + tolls), and there are four possible routes:
A= (60 min, 30€)
B= (65 min, 25€)
C= (85 min, 20€)
D= (90 min, 15€)
where (x,y) = (travel time, economic cost)
With the current version of OSRM we obtain solution A, since it is the
fastest of all. If we load an economic cost profile in OSRM, that labels
each edge with the economic cost of traversing that edge, we obtain
solution D, since it is the cheapest. What about if the user wants a
solution with better trade-off? B and C would be good solutions too.
I think an OSRM version providing the extreme solutions for each criterion
(fastest-A and most-economical-D in this case) and a small set of solutions
with "good" trade-off between both criteria would be a very interesting
feature for the project, although I'm not sure how this could be included,
since it would involve many changes and the performance in continental maps
is unknown.
Sorry for such a long mail.
PS: If someone is interested these are some academic references of papers
dealing with this problem:
Preprocessing a multicriteria algorithm for routing:
http://i11www.iti.uni-karlsruhe.de/extra/publications/dw-pps-09.pdf
Algorithm that extends A* to the Multiobjective case, keeping the same
theoretical properties than A*:
http://dl.acm.org/citation.cfm?doid=1754399.1754400
Parallelization of that algorithm:
http://algo2.iti.kit.edu/documents/Sanders%202013/ipdps.pdf
Best regards,
Francisco J.
On Tue, Mar 31, 2015 at 2:00 PM, <osrm-talk-request at openstreetmap.org>
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> Today's Topics:
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> 1. alternative route (Romain NKONGO)
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> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 31 Mar 2015 11:10:14 +0200
> From: Romain NKONGO <romain.rnk49 at gmail.com>
> To: Mailing list to discuss Project OSRM <osrm-talk at openstreetmap.org>
> Subject: [OSRM-talk] alternative route
> Message-ID:
> <CAAwSghEqK-w+MQ+kdi3r9hPKvv6tuZ0FFT1Nq9cDH3t_wLOX=
> g at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hello everyone,
>
> I've succeeded to add a new criterion called cyclability to OSRM, which is
> associated with each edge in the graph. It is created in bicycle.lua file
> and I managed to bring it all through the processing phase and to make a
> mean value on each segment of the shortest path. In the JSON, I now have a
> 9th value for each element in route instructions and a mean value in route
> summary.
>
> Now I intend to add a bicriteria algorithm to the routing phase (based on
> Label Setting). Such an algorithm would return multiple paths as results to
> one viaroute query. The problem is the original implementation allows 2
> routes at most to be returned.
>
> Has anyone tried to increase the limit of routes returned? If not, what is
> the condition for an alternative route and is there at least a way to force
> OSRM to show an alternative route?
>
> Thanks in advance for the help.
> Romain NKONGO.
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