[Qgis-user] Shortest path caching

[DelazJ]

Hi,

Le lun. 16 sept. 2019 à 15:25, Nicolas Cadieux <nicolas.cadieux at archeotec.ca>
a écrit :

> Hi,
>
> You could go with NetworkX, a python library.  With that, you can build
> the graph on the fly and maintain it as roads or edges get added and
> removed.
>
> You can probably do this with QGIS but the biggest problem I found with
> QGIS is the lack of documentation for using the network analysis tools
> using the latest versions. Everything is, or was documented for version
> 2.x.  Also, when using the processing tools in a batch, the graph gets
> rebuilt every time this should not happen.
>
> Nicolas, about the lack of documentation, you meant the tools in the
processing toolbox [0] or the pyQGIS cookbook [1]. I'm not sure there's
anything missing in the former (and maybe Paul could find some answers)
and, for the latter (which is horribly outdated), it's the usual lack of
skilled people to provide necessary documentation. Because some parts of
the docs are specialized, they require advanced users to help us update. If
we are giving a txt (or whatever open format) file updating the section,
I'm happy to push it and update that page too.

[0]
https://docs.qgis.org/testing/en/docs/user_manual/processing_algs/qgis/networkanalysis.html
[1]
https://docs.qgis.org/testing/en/docs/pyqgis_developer_cookbook/network_analysis.html

Regards,
Harrissou

> For those reasons, I went with NetworkX python library.  Out of curiosity,
> how many edges are you dealing with? How many queries?
>
> Nicolas
>
>
>
>
>
> Le 16 sept. 2019 à 08:03, Paul Wittle <paul.wittle at dorsetcouncil.gov.uk>
> a écrit :
>
> Hi,
>
>
>
> I’m aware that you can use things like the pgRouting plugin for shortest
> path calculations but when looking at the default functions is there a
> sensible way to speed up the calculations?
>
>
>
> I’ve just run a couple of tests using an Oracle database based routing
> layer and it runs but seems to take a long time to build the graph. I
> wondered if there is a plugin which stores some sort of optimised network
> to speed up the process or perhaps a type of index I could put on the
> network?
>
>
>
> At present the network is big so I guess perhaps some form of clip then
> run process might be helpful?
>
>
>
> I just thought I’d email to see what others do as I’ve not looked at
> routing in QGIS for some years now and I’d prefer to avoid more complex
> options such as pgRouting if possible.
>
>
>
> Thanks,
>
> Paul
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