Thank you for your answer.nAt the end I looked at the picture in the reference and I made it work. The facet is defined correctly if the vertice sequence identifies the outer normal vector to the facet. Similarly if I want to draw a hole in an existing facet I must define the vertices sequence such that they describe the inner normal to the figure.nActually this mechanism should be more explicit in the documentation in my opinion, it would save a lot of time .n