stitch_borders_example output error

[citystrawman]

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Issue Details

I am studying the polygon mesh processing stitch_borders_example, and I think this example shows that by using stitch_borders(), it will stitch the duplicated nodes, I ran this program and from the off file we can see that it actually does merge duplicated nodes:

quads_to_stich.off:
OFF
20 8 0
1 0 0
0.75 0 0
0.5 0 0
0.25 0 0
0 0 0
0 1 0
0.25 1 0
0.5 1 0
0.75 1 0
1 1 0
1 1 0
0.75 1 0
0.5 1 0
0.25 1 0
0 1 0
0 2 0
0.25 2 0
0.5 2 0
0.75 2 0
1 2 0
4  5 6 3 4
4  3 6 7 2
4  1 2 7 8
4  1 8 9 0
4  15 16 13 14
4  13 16 17 12
4  11 12 17 18
4  11 18 19 10

mesh_stitched.off:
OFF
15 8 0

1 0 0
0.75 0 0
0.5 0 0
0.25 0 0
0 0 0
0 1 0
0.25 1 0
0.5 1 0
0.75 1 0
1 1 0
0 2 0
0.25 2 0
0.5 2 0
0.75 2 0
1 2 0
4  5 6 3 4
4  3 6 7 2
4  1 2 7 8
4  1 8 9 0
4  10 11 6 5
4  6 11 12 7
4  8 7 12 13
4  8 13 14 9

however, in the terminal output, it is shown as follows:

Before stitching :
         Number of vertices  :  15
         Number of halfedges :  44
         Number of facets    :  8
Stitching done :
         Number of vertices  :  15
         Number of halfedges :  44
         Number of facets    :  8

I dont know if this is a bug ?

Source Code

Environment

• Operating system (Windows/Mac/Linux, 32/64 bits):
• Compiler:
• Release or debug mode:
• Specific flags used (if any):
• CGAL version:
• Boost version:
• Other libraries versions if used (Eigen, TBB, etc.):

[MaelRL]

You are probably using a CGAL::Surface_mesh and getting the number of elements through num_vertices() and similar functions.

As the doc indicates:

num_vertices() may return a number larger than std::distance(vertices(g).first, vertices(g).second). This is the case for implementations only marking vertices deleted in the vertex container.

This is because the surface mesh will have "garbage" (i.e., removed elements) after calling PMP::stitch_borders duplicate elements have been removed during stitching. In CGAL::Surface_mesh, these are not purged from memory unless you call collect_garbage() and thus the number of elements through num_vertices(sm) is unchanged.

If you want the exact number of elements without collecting garbage, you can use the number_of_vertices member function of the CGAL::surface_mesh, or std::distance(...), or vertices(sm).size(), or CGAL::internal::exact_num_vertices(sm), ...

[citystrawman]

You are probably using a CGAL::Surface_mesh and getting the number of elements through num_vertices() and similar functions.

As the doc indicates:

num_vertices() may return a number larger than std::distance(vertices(g).first, vertices(g).second). This is the case for implementations only marking vertices deleted in the vertex container.

This is because the surface mesh will have "garbage" (i.e., removed elements) after calling PMP::stitch_borders duplicate elements have been removed during stitching. In CGAL::Surface_mesh, these are not purged from memory unless you call collect_garbage() and thus the number of elements through num_vertices(sm) is unchanged.

If you want the exact number of elements without collecting garbage, you can use the number_of_vertices member function of the CGAL::surface_mesh, or std::distance(...), or vertices(sm).size(), or CGAL::internal::exact_num_vertices(sm), ...

but the output shows the numbe of vertex after stitching, not before stitching, which is weired. (I just use the code pulled from git, the branch is 5.5.x)