Re: [igraph] Building a graph from a picture

[Sadz A]

I'm not sure what you mean by 'how' I want to convert the shapefile to a graph:

The data I have is a road map that I digitised from a satellite image in ArcGIS, if I convert it to an ascii that R can read I suppose it would be a grid of no-value pixels, with the roads being represented as value pixels. 

I would like nodes to be the points at which two lines cross or a road turns at a right angle, and, I would like the edges to simply be how the various nodes are connected, they do not need to be directional or contain information on flow etc. I would also like to get a matrix out that shows how the network is build, for example point a and b are connected by edge 1, and point a and c are connected by edge 2. 

I'm very new to network analyses, but I think what I would like to then do is compare several of my digitised road maps (after converting them to matrices and graphs) by calculating connectivity, network stability etc. 

Thank you

ps- I will try the R sig spatial list, but I though igraph was used to carry out network analysis and draw graphs of networks. 

---

From: Jacob van Etten <address@hidden>
To: Help for igraph users <address@hidden>
Sent: Fri, 3 December, 2010 4:46:59
Subject: Re: [igraph] Building a graph from a picture

Well, this depends on HOW you want to convert the shapefile to a graph
(what should the edges and vertices represent?).

I think it would be better to ask this question on the r-sig-spatial
list, specifying a bit more what type of data you have and what you
want to do.

2010/12/2 Sadz A <address@hidden>:
> I have some networks in GIS shape file (vector) format (I can change them to
> raster or Ascii), is there a way to convert them into matrix or graph that
> can be loaded and analysed with igraph in R?
> Any help is really appreciated
> Thank you
>
> _______________________________________________
> igraph-help mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/igraph-help
>
>

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