[Qgis-user] Support - representing a graph in Qgis

[Jorge Gustavo Rocha]

Hi Giacomo,

Maybe it is better to share a sketch of what you want.

0) From the description of your use case, you can use the geographic
position of the nodes, right? You might be able to do what you want just
by creating points where you want to show the grid voltage and then
create direct lines between nodes. If you can display it on the map, you
don't need a graph.

1) Yes, you can use graphviz in the python console.

2) Graphviz does not read shapefiles. You have to iterate over your
layer and generate the corresponding graph nodes and edges.

Regards,

Jorge Gustavo

Às 23:06 de 09/02/21, Giacomo Uguccioni escreveu:
> Thank you guys for the support.
> Could I work with Graphviz in the python console inside Qgis? And does
> Graphviz support shapefiles or similar as an input? 
>
> Il giorno mar 9 feb 2021 alle 20:07 Jorge Gustavo Rocha
> <jgr at geomaster.pt <mailto:jgr at geomaster.pt>> ha scritto:
>
>     Hi,
>
>     I second Chris's proposal. Using graphviz python module [1], you
>     can generate your graph by iterating over the features.
>
>     At the end, just call the render and you will get the rendered
>     graph (just add view=True) within your QGIS environment. You need
>     to know some Python basic stuff, but not much than the basic.
>
>     Regards,
>
>     Jorge Gustavo
>
>     [1] https://graphviz.readthedocs.io/en/stable/manual.html
>
>     Às 18:55 de 09/02/21, chris hermansen escreveu:
>>     Giacomo and list,
>>
>>     On Tue, Feb 9, 2021 at 8:07 AM Giacomo Uguccioni
>>     <giacomo.uguccioni at gmail.com
>>     <mailto:giacomo.uguccioni at gmail.com>> wrote:
>>
>>         Hello everyone, and thanks for the support.
>>         If this is not the place to ask for this kind of thing, I ask
>>         you to give me a link where I could find support.
>>         I'm a qgis 3.14 user. I would like to represent a tree
>>         diagram or functional diagram being able to draw the
>>         symbology and position of nodes and connections from the
>>         information contained in the attribute table. Example: I
>>         would like to represent the medium voltage grid of a city as
>>         an electrical diagram; I would like to represent with lines
>>         that join at nodes the roads that connect certain houses and
>>         schools in a city. So my goal is to be able to build a layout
>>         with symbology of nodes and connections derived from
>>         information contained in different shapefiles or within
>>         features, with a non-geographic but schematic / ideal criterion.
>>         Do you have any ideas or suggestions on how to do it? I thank
>>         you for every contribution.
>>
>>
>>     Not a QGIS-based solution, but I've used graphviz
>>     <https://graphviz.org/> to generate graphs from the command line
>>     with considerable success.  It offers a small but useful
>>     programming language that can be combined with data in text files
>>     in a really useful way.
>>
>>     -- 
>>     Chris Hermansen · clhermansen "at" gmail "dot" com
>>
>>     C'est ma façon de parler.
>>
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