Cgal 表面网格 - 连通性

Question

我有点困惑连接是如何工作的。我正在尝试从网格中移除面，并调整连接性，移除未使用的边和顶点。当我使用 mesh.is_valid() 它显示连接问题

Integrity of previous halfedge of h1 corrupted. Halfedge of v0 is not an incoming halfedge. vertices: iterated: 1 vs number_of_vertices(): 5 halfedges: iterated: 2 vs number_of_halfedges(): 14 faces: iterated: 3 vs number_of_faces(): 3

代码：

#include <string>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/Surface_mesh.h>
#include <boost/foreach.hpp>
#include <iostream>
#include <CGAL/Simple_cartesian.h>
#include <CGAL/Gmpq.h>
#include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
typedef CGAL::Exact_predicates_inexact_constructions_kernel K;

typedef CGAL::Surface_mesh<K::Point_3> Mesh;
typedef Mesh::Vertex_index vertex_descriptor;
typedef Mesh::Face_index face_descriptor;
typedef Mesh::Halfedge_index halfedge_descriptor;
typedef Mesh::Edge_index edge_descriptor;

int main()
{
  Mesh mesh;
  vertex_descriptor v0 = mesh.add_vertex(K::Point_3(0,2,0));
  vertex_descriptor v1 = mesh.add_vertex(K::Point_3(2,2,0));
  vertex_descriptor v2 = mesh.add_vertex(K::Point_3(0,0,0));
  vertex_descriptor v3 = mesh.add_vertex(K::Point_3(2,0,0));
  vertex_descriptor v4 = mesh.add_vertex(K::Point_3(1,1,0));
  mesh.add_face(v3, v1, v4);
  mesh.add_face(v0, v4, v1);
  mesh.add_face(v0, v2, v4);
  mesh.add_face(v2, v3, v4);

 int counter = 0;
 std::vector <edge_descriptor> edg;
 BOOST_FOREACH(face_descriptor fd, mesh.faces()){
  if(counter == 0){
    halfedge_descriptor hed = mesh.halfedge(fd);
    halfedge_descriptor prev = mesh.prev(hed);
    halfedge_descriptor next = mesh.next(hed);

    mesh.set_vertex_halfedge_to_border_halfedge (next);
    mesh.set_vertex_halfedge_to_border_halfedge (prev);
    mesh.set_vertex_halfedge_to_border_halfedge (hed);

    if(mesh.is_border(mesh.opposite(next))){
      mesh.remove_edge(mesh.edge(next));
      std::cout << "Remove next halfedge " << next << std::endl;
    }else{
      mesh.set_face(next, mesh.null_face());
      std::cout << "sets next halfedge " << next << std::endl;
    }

    if(mesh.is_border(mesh.opposite(prev))){
      mesh.remove_edge(mesh.edge(prev));
      std::cout << "Remove prev halfedge " << prev << std::endl;
    }else{
      mesh.set_face(prev, mesh.null_face());
      std::cout << "sets prev halfedge " << prev << std::endl;
    }
    if(mesh.is_border(mesh.opposite(hed))){
      mesh.remove_edge(mesh.edge(hed));
      std::cout << "Remove Face halfedge " << hed << std::endl;
    }else{
      mesh.set_face(hed, mesh.null_face());
      std::cout << "sets Face halfedge " << hed << std::endl;
    }
    mesh.remove_face(fd);
    counter++;

    }
  }
  mesh.collect_garbage();
  mesh.is_valid();
  return 0;
}

Answer 1

使用remove_face function of the Euler operations. It will "maintain the validity" behind the scenes for you. The Euler operations work on values of any type Graph that is "a model of" MutableFaceGraph. Fortunately, your SurfaceMesh就是这样的模型。

如果您将循环（这是不必要的，因为您只想要一张脸）替换为以下内容，您将看到它是如何工作的：

int counter = 0;
BOOST_FOREACH(face_descriptor fd, mesh.faces()){
  counter++;
}
std::cout << counter << " faces" << std::endl;

CGAL::Euler::remove_face(mesh.halfedge(*mesh.faces().begin()), mesh );
mesh.collect_garbage();
mesh.is_valid();

counter = 0;
BOOST_FOREACH(face_descriptor fd, mesh.faces()){
  counter++;
}
std::cout << counter << " faces" << std::endl;

这不会产生验证错误，并确认操作后网格中少了一个面。

Cgal 表面网格 - 连通性

Cgal surface mesh - connectivity

c++

mesh

cgal