How is such a tool going to establish whether a face is 'inside' or 'outside' a form ? It'd be possible with a 'solid', but with loose faces who is to say what is the right way round ? There are several 'face reversing' tools around - open the 'Plugins Index' page and use your browser's search for 'reverse' or 'flip' etc... Find one that suits you... I think Didier's tool reverses all 'backwards' active faces that are looking at the current camera, which might do what you want best...

Thanks, Thomthom . I'll follow your advice.

@thierry_st_malo said: It works for the red and the green axis, but not for the blue one. Ridiculously, I can't see why. What you explain more what "doesn't work"? Exactly what happens, and what did you expect? Any errors?

@thierry_st_malo said: It was a kind of smoothing that I was looking for. I have two plugins on my blog that might help you. The first is EqSegCurve which allows you to specify either a number of segments or segment length. The input segment length will be adjusted as required if length is entered. The second is Spline which adds interpolated points to smooth the curve. Your model is attached with an example of each. Essai.skp

Rectification, désolé ce n'est pas une erreur systématique. Il y en a une autre qui n'est pas systématique non plus, avec le rendu de scènes visualisées dans Sketchup en projection orthogonale. Thierry*

Thanks very much, TIG