在CGAL中创建3D Alpha形状及其可视化 我是一个新的CGAL用户，有C++的基本经验，试图找到一组点的3D alpha形状。我正在使用示例代码，然后使用中的说明对结果进行可视化。一切似乎都正常工作，但当我试图通过替换 Alpha_shape_3 as(lp.begin(),lp.end());

与

假设第三个变量是alpha（=1）的值，并且每次更改该值，则结果不会发生任何更改

更具体地说，在我的粒子集中，一些粒子与大多数粒子分离，我希望使用凹面外壳或alpha形状使用单独的体积（类似于）来表示它们。目前我得到的（使用Tecplot进行可视化）是： 如你所见，分离的粒子与其他粒子相连。我也附上我的代码，在最后。在这件事上，如果有任何帮助，我将不胜感激

    #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
    #include <CGAL/Delaunay_triangulation_3.h>
    #include <CGAL/Alpha_shape_3.h>

    #include <iostream>
    #include <fstream>
    #include <list>
    #include <cassert>

    typedef CGAL::Exact_predicates_inexact_constructions_kernel Gt;

    typedef CGAL::Alpha_shape_vertex_base_3<Gt>          Vb;
    typedef CGAL::Alpha_shape_cell_base_3<Gt>            Fb;
    typedef CGAL::Triangulation_data_structure_3<Vb,Fb>  Tds;
    typedef CGAL::Delaunay_triangulation_3<Gt,Tds>       Triangulation_3;
    typedef CGAL::Alpha_shape_3<Triangulation_3>         Alpha_shape_3;

    typedef Gt::Point_3                                  Point;
    typedef Alpha_shape_3::Alpha_iterator               Alpha_iterator;

    using namespace std;

    int main()
    {
      std::list<Point> lp;

      //read input
      std::ifstream is("./data/finalwater4.dat");
      int n;
      is >> n;
      std::cout << "Reading " << n << " points " << std::endl;
      Point p;
      for( ; n>0 ; n--)    {
        is >> p;
        lp.push_back(p);
      }

      // compute alpha shape
    //  Alpha_shape_3 as(lp.begin(),lp.end());
      Alpha_shape_3 as(lp.begin(),lp.end(),0.001, Alpha_shape_3::GENERAL);

      // find optimal alpha value
      Alpha_iterator opt = as.find_optimal_alpha(1);
      std::cout << "Optimal alpha value to get one connected component is "
            <<  *opt    << std::endl;
      as.set_alpha(*opt);
      assert(as.number_of_solid_components() == 1);

      /// the rest of the code, prepares the output to be written into a file

      /// collect all regular facets (fetch regular facets from as and inserts in facets)
      std::vector<Alpha_shape_3::Facet> facets;
      as.get_alpha_shape_facets(std::back_inserter(facets), Alpha_shape_3::REGULAR);

      std::stringstream pts;
      std::stringstream ind;

      std::size_t nbf=facets.size();
      for (std::size_t i=0;i<nbf;++i)
      { 
        //To have a consistent orientation of the facet, always consider an exterior cell
        if ( as.classify( facets[i].first )!=Alpha_shape_3::EXTERIOR )
          facets[i]=as.mirror_facet( facets[i] );
        CGAL_assertion(  as.classify( facets[i].first )==Alpha_shape_3::EXTERIOR  );

        int indices[3]={
          (facets[i].second+1)%4,
          (facets[i].second+2)%4,
          (facets[i].second+3)%4,
        };

        /// according to the encoding of vertex indices, this is needed to get
        /// a consistent orienation
        if ( facets[i].second%2==0 ) std::swap(indices[0], indices[1]);


        pts << 
        facets[i].first->vertex(indices[0])->point() << "\n" <<
        facets[i].first->vertex(indices[1])->point() << "\n" <<
        facets[i].first->vertex(indices[2])->point() << "\n"; 
        ind << 3*i+1 << " " << 3*i+2 << " " << 3*i+3 << "\n";
      }

      ofstream myfile;
      myfile.open ("output.dat");
      myfile << "variables = x, y, z\n";
      myfile << "zone n="<< 3*nbf << " , e=" << nbf << " , f=fepoint, et=triangle\n";
      myfile << pts.str();
      myfile << ind.str();
      myfile.close();

      return 0;
    }

#包括
#包括
#包括
#包括
#包括
#包括
#包括
typedef CGAL:：精确谓词不精确结构内核Gt；
typedef CGAL:：Alpha_形状_顶点_底面_3 Vb；
typedef CGAL:：Alpha_形状_单元_基底_3 Fb；
typedef CGAL:：三角测量数据结构Tds；
typedef CGAL:：Delaunay_三角剖分_3三角剖分_3；
typedef CGAL:：Alpha_shape_3 Alpha_shape_3；
类型定义Gt：：点_3点；
typedef Alpha_shape_3:：Alpha_迭代器Alpha_迭代器；
使用名称空间std；
int main（）
{
std：：list-lp；
//读取输入
标准：：如果流是（“./data/finalwater4.dat”）；
int n；
是>>n；
std:：cout如果你想过滤掉东西，你需要采用一个alpha形状，它的值小于as.find_optimal_alpha（1）返回的值。我建议运行alpha形状演示，该演示具有一个滑块，该滑块将根据alpha的值显示alpha形状的外观。输入文件的扩展名应为.pts，并且必须包含点数，后跟点的坐标。
非常感谢您的回复。我刚刚删除了该部分“找到最佳alpha值”，现在可以使用了：）
    #include <CGAL/Exact_predicates_inexact_constructions_kernel.h>
    #include <CGAL/Delaunay_triangulation_3.h>
    #include <CGAL/Alpha_shape_3.h>

    #include <iostream>
    #include <fstream>
    #include <list>
    #include <cassert>

    typedef CGAL::Exact_predicates_inexact_constructions_kernel Gt;

    typedef CGAL::Alpha_shape_vertex_base_3<Gt>          Vb;
    typedef CGAL::Alpha_shape_cell_base_3<Gt>            Fb;
    typedef CGAL::Triangulation_data_structure_3<Vb,Fb>  Tds;
    typedef CGAL::Delaunay_triangulation_3<Gt,Tds>       Triangulation_3;
    typedef CGAL::Alpha_shape_3<Triangulation_3>         Alpha_shape_3;

    typedef Gt::Point_3                                  Point;
    typedef Alpha_shape_3::Alpha_iterator               Alpha_iterator;

    using namespace std;

    int main()
    {
      std::list<Point> lp;

      //read input
      std::ifstream is("./data/finalwater4.dat");
      int n;
      is >> n;
      std::cout << "Reading " << n << " points " << std::endl;
      Point p;
      for( ; n>0 ; n--)    {
        is >> p;
        lp.push_back(p);
      }

      // compute alpha shape
    //  Alpha_shape_3 as(lp.begin(),lp.end());
      Alpha_shape_3 as(lp.begin(),lp.end(),0.001, Alpha_shape_3::GENERAL);

      // find optimal alpha value
      Alpha_iterator opt = as.find_optimal_alpha(1);
      std::cout << "Optimal alpha value to get one connected component is "
            <<  *opt    << std::endl;
      as.set_alpha(*opt);
      assert(as.number_of_solid_components() == 1);

      /// the rest of the code, prepares the output to be written into a file

      /// collect all regular facets (fetch regular facets from as and inserts in facets)
      std::vector<Alpha_shape_3::Facet> facets;
      as.get_alpha_shape_facets(std::back_inserter(facets), Alpha_shape_3::REGULAR);

      std::stringstream pts;
      std::stringstream ind;

      std::size_t nbf=facets.size();
      for (std::size_t i=0;i<nbf;++i)
      { 
        //To have a consistent orientation of the facet, always consider an exterior cell
        if ( as.classify( facets[i].first )!=Alpha_shape_3::EXTERIOR )
          facets[i]=as.mirror_facet( facets[i] );
        CGAL_assertion(  as.classify( facets[i].first )==Alpha_shape_3::EXTERIOR  );

        int indices[3]={
          (facets[i].second+1)%4,
          (facets[i].second+2)%4,
          (facets[i].second+3)%4,
        };

        /// according to the encoding of vertex indices, this is needed to get
        /// a consistent orienation
        if ( facets[i].second%2==0 ) std::swap(indices[0], indices[1]);


        pts << 
        facets[i].first->vertex(indices[0])->point() << "\n" <<
        facets[i].first->vertex(indices[1])->point() << "\n" <<
        facets[i].first->vertex(indices[2])->point() << "\n"; 
        ind << 3*i+1 << " " << 3*i+2 << " " << 3*i+3 << "\n";
      }

      ofstream myfile;
      myfile.open ("output.dat");
      myfile << "variables = x, y, z\n";
      myfile << "zone n="<< 3*nbf << " , e=" << nbf << " , f=fepoint, et=triangle\n";
      myfile << pts.str();
      myfile << ind.str();
      myfile.close();

      return 0;
    }