How can I constrain some edges of the surface_mesh?

KeepFaithMe commented 4 years ago

Please use the following template to help us solving your issue.

Issue Details

I want to constrain some edges of the surface_mesh.I see the document https://doc.cgal.org/latest/Surface_mesh_simplification/index.html . and Surface_mesh_simplification/edge_collapse_OpenMesh.cpp .The data struct is OpenMesh.The type of surface_mesh is: typedef OpenMesh::PolyMesh_ArrayKernelT<> surface_mesh;but I want use the 'typedef CGAL::Simple_cartesian K; typedef CGAL::Surface_meshsurfacemesh;',but the function 'add_property()' do not contain in this surface_mesh. So if I want use the '_typedef CGAL::Simple_cartesian K; typedef CGAL::Surface_meshsurfacemesh',what should i do?

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sloriot commented 4 years ago

In the simplification function documentation, you will see that there is the named parameter edge_is_constrained_map that can be used to pass some constrained edges to the algorithm. You also need to use the Constrained_placement to wrap you current placement.

Here is an example where sharp edges of a Polyhedron are constrained. You can adapt it to make it work with OpenMesh.

KeepFaithMe commented 4 years ago

I have another question! I can read the .obj data,and I want convert the .obj data to Polyhedron_3,at the same time do the operation of simplification. I use the function 'make_triangle()' to construct Polyhedron_3,but when I do the simplification,there is a bug ,I do'nt konw what's wrong with the code?And I check out the output data, the vertices chabged.For example,in the .obj file,the number of vertices is 351,but in the new .off file is 1662.I konw the vertices is repeat,but I do'nt konw why? the Code :

#include <CGAL/Simple_cartesian.h>
#include <CGAL/Polyhedron_3.h>
#include <CGAL/Polyhedron_items_with_id_3.h>
#include <CGAL/Surface_mesh_simplification/edge_collapse.h>
#include <CGAL/Surface_mesh_simplification/Policies/Edge_collapse/Count_ratio_stop_predicate.h>
typedef  CGAL::Simple_cartesian<double> Kernel;
typedef  Kernel::Point_3 Point_3;
typedef CGAL::Polyhedron_3<Kernel, CGAL::Polyhedron_items_with_id_3> surface_mesh;
typedef boost::graph_traits<surface_mesh>::halfedge_descriptor halfedge_descriptor;
typedef boost::graph_traits<surface_mesh>::vertex_descriptor vertex_descriptor;
for (int i = 0; i < aMesh->mIndices.size(); i += 3)
    {
        Point_3 p1 = Point_3(aMesh->mVertices[aMesh->mIndices[i]].x, aMesh->mVertices[aMesh->mIndices[i]].y, aMesh->mVertices[aMesh->mIndices[i]].z);
        Point_3 p2 = Point_3(aMesh->mVertices[aMesh->mIndices[i + 1]].x, aMesh->mVertices[aMesh->mIndices[i + 1]].y, aMesh->mVertices[aMesh->mIndices[i + 1]].z);
        Point_3 p3 = Point_3(aMesh->mVertices[aMesh->mIndices[i + 2]].x, aMesh->mVertices[aMesh->mIndices[i + 2]].y, aMesh->mVertices[aMesh->mIndices[i + 2]].z);
        SMesh.make_triangle(p1, p2, p3);
    }

the aMesh save the vertices ,indeics,etc,not the surface_mesh.

sloriot commented 4 years ago

Use the function

template <class Point_3>
bool
read_OBJ( std::istream& input,
          std::vector<Point_3> &points,
          std::vector<std::vector<std::size_t> > &faces)

in CGAL/IO/OBJ_reader.h together with the function polygon_soup_to_polygon_mesh().

CGAL / cgal