Hi!!! I don’t undertstand how to get a negative extract: I mean, painting a mask on a surface, then the extract go “into” the surface, the upper part being at the same level than the original surface… When I try to use negative values, in fact there is a part of the extract wich is “out”, and the normals seems to be disturbed (which is easy to solve, I Agree, with double polys face)… Thank you for help!!!
Hello @marcel
The mesh extract function does not change the surface of the source mesh–it only creates a new mesh. So if you set it to to a negative thickness, you are going to generate the new mesh underneath the surface of your mesh, and bits of it might poke through, depending on the differences between the surfaces.
Options like double will resort in an even larger extract that extrudes in both directions, so even more of that will show.
If your operation results in a mesh with flipped normals, you can flip these back with tool > Display > Flip.