[Gmsh] stl and prism extrusion

[Hoessler, Julien]

Good afternoon all,
First of all, thanks for writing this code, I'm using it a lot to generate 2D/3D meshes for DNS and stability analysis. I was wondering if it is possible to extrude a layer of prisms using the surface normals instead of a specific direction. I need to generate a layer of prisms out of a wall which is curved and there is more than 80 degrees of angular difference between the two extreme locations of the surface (it is smooth, but twists a bit like a sinh). 
My second question is about the stl importation. I have a stl file which is a 3D box that I can read and visualise without problems, but I'd like to remesh it, mesh the volume inside  and split the box surface to assign different physical groups for boundary conditions (and add a layer of prisms on one of the surfaces). Is it possible with Gmsh? I've searched through the questions in this mailing list, do I need the opencascade support for this?
Thanks for your help
Best regards

Julien Hoessler
PhD student,
Department of Aeronautics,
Imperial College London,
South Kensington Campus