# [pgrouting-users] improve performance of isoline computation

Mayeul KAUFFMANN mayeul.kauffmann at jrc.ec.europa.eu
Tue Jun 7 06:37:09 EDT 2011

```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

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
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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