Re: [igraph] Graph Visualization

[Tamas Nepusz]

Hi Lorenzo,

IMHO the first step in creating a decent visualization is to find a  
layout of the vertices that pleases the eye. If your vertices are  
particles in 2D or 3D space, you might use their coordinates directly;  
if not, a good choice is the DrL layout algorithm, which is  
unfortunately not yet implemented in igraph (although you can create a  
Python wrapper that saves the graph in edgelist format, passes it to  
DrL by directly calling its executable and then parse the resulting  
layout file to obtain a Layout object).
See the following page for the source code of DrL:
http://www.cs.sandia.gov/~smartin/software.html

After having obtained a satisfactory layout, you can use the plot  
command in Python to plot the graph:

plot(g, layout=lo)

where `g' is the graph being visualized and `lo' is the Layout object  
or the name of a built-in visualization algorithm (see  
help(Graph.layout) for a list of known layouts). This draws the graph  
according to the layout in a temporary .png file and opens it in the  
image viewer of your OS. Vertex sizes can be controlled by assigning  
to the "size" vertex attribute, colors can be controlled by assigning  
to the "color" vertex attribute. The "color" attribute may either  
contain color specifications in "#rrggbb" format (as in HTML), or an  
integer between 0 and 255 which refers to the current color palette of  
the plot (see help(Palette), help(GradientPalette),  
help(AdvancedGradientPalette) and the "palette" keyword argument of  
plot).

Plots can also be saved permanently, e.g.:

g = Graph.Tree(156, 5)
plot(g, "graph.png", layout="fruchterman_reingold", vertex_label=None)


--
Tamas