[vtkusers] How to extract the contour of an unstructured grid ?

[Hummel, Jerome]

Sorry if this is an easy question but it is possible to do to this ?
I have an unstructured grid and I only would like to see the skin of it and more
precisely the wireframe of the skin.
I want to hide any cells that are within the grid and only keep the bounds.
To keep it simple lets say I have 4 triangles sharing the same vertex and
ordered as a square.
Te filter should output a square shape.
Thanks a lot for your help,

-Jerome