Add swept extrusion

[sloriot]

fixes #6292

[sancelot]

I tried it , I had this compilation error
E:/WORKSPACE/cgal/Polygon_mesh_processing/examples/Polygon_mesh_processing/create_bended_cylinder.cpp:52:8: error: 'sweep_extrude' is not a member of 'PMP'
52 | PMP::sweep_extrude(mesh, guide, out);
| ^~~~~~~~~~~~~

[sloriot]

No idea how you compiled it but this PR modifies 2 CGAL headers, one of them contains that function.

[sancelot]

I compiled using msys2 mingw64 compiler.

Removing this line compiles.

[sloriot]

I mean, you either need to add the modified headers in the compilation unit (before those of the release) or use the branch to compile the example.

[sancelot]

I am using your branch ... this is why I don't really understand ...

[sloriot]

The way I would debug that is to put a typo in the header file you think is used and see if the compilation fails at that point. You can also grep CGAL_DIR in CMakeCache.txt, ...

[sancelot]

OK. I found the pb, it was using a conflicting cgal header installed in the system.
Thanks.

[FuzhangHe]

Hallo Sloriot,

Firstly, thank you for the sweep function, it is really useful.

In my case, it is difficult to calculate the guidelines. But I know the start face mesh, the rotation angle, and translation, so I can calculate the end face mesh. Is there any method to construct a surface mesh with the start face mesh and end face mesh?
I think it is the same as sweep, but not with guideline.

[sloriot]

@FuzhangHe if it is only a translation, I guess you can sample le translation and interpolate the rotation to get something smooth.

[FuzhangHe]

Hello, Sloriot,

Thank you for the quick reply.
For my case, it is only a simple rotation:

I have tried the following code with the PMP::sweep_extrude function:

  Mesh mesh;

  // Add the points as vertices
  vertex_descriptor u = mesh.add_vertex(K::Point_3(0, 1, 0));
  vertex_descriptor v = mesh.add_vertex(K::Point_3(0, 2, 0));
  vertex_descriptor w = mesh.add_vertex(K::Point_3(0, 2, 1));
  vertex_descriptor x = mesh.add_vertex(K::Point_3(0, 1, 1));
  face_descriptor f = mesh.add_face(u, v, w, x);

  std::vector<Point_3> guide;

  for (int i=0; i<7; ++i)
    guide.push_back(Point_3(2*std::sin(2 * CGAL_PI / 24 * i), 2 * std::cos(2 * CGAL_PI / 24 * i),  0));

The result is shown in the following foto. It can be seen, that it has been rotated slightly more than 90°. When I refine the rotation angle, the result will be better.

To my question:
I know how to interpolate the rotation of a face mesh, but I do not know how to connect the face meshes to a new surface mesh. Should I do something like the extrude_impl::create_strip as in the extrude.h ?

[sloriot]

You should indeed create intermediate contours stored in the code in current_hedges and incrementally add strips using extrude_impl::create_strip(). Look around https://github.com/CGAL/cgal/pull/6317/files#diff-55f2604e6a010faeeb37e6e4ce1e05b11d71cfdcc12e35c3aebbbdd911c644cdR500