[Qgis-developer] Network analysis

[Mark Wynter]

I'd also recommend igraph.
Description below describes how I'm using igraph (cut and paste from an earlier private email conversation).

I still use grass for some aspects of topology cleaning (eg messy OSM data), but igraph thereafter.

This is how I'm using igraph currently...

>> I use igraph directly from postgis via pl/r wrappers. I use it mainly for least cost routing instead of pgrouting. Besides igraph being a very fast routing engine, it opens up possibilities to embed the inputs or outputs within other analytics processes or visualizations.
>> 
>> I've written igraph postgis functions that take
>> wkb_geoms and build an igraph directed network object.
>> 
>> Other postgis custom functions then query the network and return
>> -Node to node Shortest path
>> -Node to multinode shortest paths
>> -Mode - inward vs outward directed shortest paths
>> - travel distance matrices
>> -all of the above using R's parallel computing capabilities
>> - anything else which canbe done in igraph or R, and returned to Postgresql/postgis.
>> 
>> I then use the results to build polylines, isochrones and cost surfaces on the fly using the new KNN lateral query pattern in postgis.
>> 
>> And when you create a Postgis materialized view that calls these igraph functions, we can present dynamic QGIS visualizations. So if you drag the location of a hospital in QGIS, you see the postgis isochrones or accessibility surface immediately update when you hit save.
>> 
>> The other thing to bear in mind is that igraph also comes as a python library so you might be able to mash up the line graphs into a QGIS panel - and instead of calling igraph in postgis via pl/r, you call it via pl/Python.  Arguably you don't need postgis if you can access the igraph Python lib directly from qgis.

> My recommendation would be igraph (http://igraph.org/).
> Powerful, Open Source (https://github.com/igraph), well documented, and comes with Python, and C++ and R interfaces.
> I used it in the r.connectivity.network addon for GRASS 6 and was quite happy with it!
> 
> Cheers
> Stefan
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