[Qgis-developer] Network analysis

[Nathan Woodrow]

Thanks a lot everyone.  Don't need it for a project at the moment but
looking around for a client.

On Fri, Jun 19, 2015 at 8:50 AM, Mark Wynter <mark at dimensionaledge.com>
wrote:

> 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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