Hi Pilou,

> Because the flat curves must will be curvated again!

No, they don't have to be manually curved - they stay planar and then are used to trim the surface.

That will generate a curved edge on the surface where it is intersected by the planar trim curve projection. That's all built into Trim, you just cut the surface (after untrimming the surface to prepare it for new trimming) with the planar curves and that's done.

- Michael