Force graph to be undirected

[Voituret Félix <felix.voituret AT univ-avignon.fr>]

Hello,

I'm currently use GraphStream for a research project where i need to 
display a transportation network,
using the MATSim framework data structure.

I wrote a custom Graph structure that extends the AbstractGraph class so 
as to interface with this data structure. That is actually working well, 
but the thing is, with the basic viewer, the graph was drawn as an 
undirected graph which fit well with the purpose. Since i set the viewer 
as the advanced one, the graph is now drawn as a directed graph as you 
can see is the attached picture.

So i would like to now if there is any way to force the graph to be 
drawn as a undirected graph (well, mix two edges between two nodes) when 
i use the advanced viewer.

Regard.
Félix Voituret.

Attachment: rendering.png
Description: PNG image