[pgrouting-users] Re: improve performance of isoline computation

[Jaak Laineste]

Hello,.

 Pgrouting can find one isoline, this is the result of driving_distance. This gives number of points, if you connect them you'll get isoline. If you need many isolines, then you should call it many times, like for 5,10,20 minutes, for same point(s) etc. It is sub-optimal this way also, but it is fast, below second for single iteration, and for most uses sufficient.

 My recent test with it (isolines from certain point in certain distances, in KML format): http://maps.google.com/?q=http://46.51.131.48/dd/index.php?lat=59.43475%26lon=24.74786%26dist=1,2,3,4,5

 Or maybe I misunderstood what exactly do you mean by isoline here?

Jaak


On 07.06.2011, at 19:00, pgrouting-users-request at lists.osgeo.org wrote:
> 
> Message: 1
> Date: Tue, 07 Jun 2011 12:37:09 +0200
> From: Mayeul KAUFFMANN <mayeul.kauffmann at jrc.ec.europa.eu>
> Subject: [pgrouting-users] improve performance of isoline computation
> To: pgrouting-users at lists.osgeo.org
> Message-ID: <1307443029.10348.130.camel at ISFLXMK2>
> Content-Type: text/plain; CHARSET=US-ASCII
> 
> Hi,
> 
> 1. I've seen at http://www.pgrouting.org/ that "pgRouting provides
> functions for [...] Driving Distance calculation (Isolines)".
> But I could not find any documentation on this (or I misunderstood
> "isolines")
> 
> In the past I have been doing this using pgrouting with this iterative
> algorithm (written in bash and allowing parallelism) which is quite
> costly:
> To compute isoline with departure from A, compute travel time between A
> and any point of the network.
> 
> This is quite similar to this:
> http://underdark.wordpress.com/2011/02/09/creating-catchment-areas-with-pgrouting-and-qgis/
> 
> http://underdark.wordpress.com/2011/05/13/catchment-areas-with-pgrouting-driving_distance/
> 
> 
> This is costly because some parts of the network get traversed many time
> by the algorithm. If point B is between A and C, then once you have
> computed the cost from A to B, you can use this piece of information to
> find the shortest path from A to C.
> 
> 
> 
> I searched for documentation here:
> http://www.pgrouting.org/docs/foss4g2010/index.html
> 
> Searching on Google:
> site:lists.osgeo.org/pipermail/pgrouting-users/ isolines
> site:lists.osgeo.org/pipermail/pgrouting-dev/ isolines
> gave no result either
> 
> 
> Are there any other solution to the isoline problem that I'm not aware?
> 
> 2. Finally, my ultimate goal is as follows:
> given a set of many departure points d1 to d1000, for each of them, find
> which of the arrival points (A, B, C, D, E) is the shortest one.
> 
> My idea would be to use the following approach, but modified:
> http://underdark.wordpress.com/2011/05/13/catchment-areas-with-pgrouting-driving_distance/
> 
> with modification as follows: after finding the best path from d1 to A,
> if this costs 100, you can search the best path from d1 to B stopping
> the search when the cost is larger than 100.
> 
> Is any of the two above problems already implemented in compiled code,
> or the best I can do is to write my own code based on shortest_path() or
> driving_distance() ?
> 
> Thanks for any help!!
> Mayeul
> 
> 
> PS: for those who wonder: this is to study the impact of transportation
> disturbance (in countries currently at war) on access to health
> infrastructure, hence: how to go to the closest hospital.
> 
> -- 
> Dr. Mayeul KAUFFMANN, Conflict Specialist
> European Commission, Joint Research Centre (JRC)
> Institute for the Protection and Security of the Citizen (IPSC)
> Global Security and Crisis Management - ISFEREA
> Via E. Fermi 2749 - I-21027 Ispra (VA), ITALY
> Phone: (+39) 033278 5071
> http://isferea.jrc.ec.europa.eu/Staff/Pages/Kauffmann-Mayeul.aspx
> 
> (Office: building 26b, 1st floor, room 140. TP: 267)
> 
> 
> 
> 
> 
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