Small example demonstrating meshing of constructive solid geometry (CSG) with Netgen via libmesh

netgen_test_04.cc

#include <iostream>
#include <fstream>
#include <map>

#include "libmesh/libmesh.h"
#include "libmesh/mesh.h"
#include "libmesh/point.h"
#include "libmesh/cell_tet4.h"

// NOTE: This example only works if you have built and installed
// netgen, (see http://sourceforge.net/projects/netgen-mesher) and you
// are using a Makefile that sets the appropriate include and library
// paths.
namespace nglib
{
#include <nglib.h>
}

using namespace libMesh;

// This code adds 2D points and line segments to a Netgen Mesh object.
int main (int argc, char** argv)
{
  // Initialize libmesh.  This is necessary because the library
  // may depend on a number of other libraries (i.e. MPI  and Petsc)
  // that require initialization before use.
  LibMeshInit init(argc, argv);
  {
    // Must be called before any other nglib functions.
    nglib::Ng_Init();

    // This code implements a slight variant of the 3D problem described in
    // http://www.asc.tuwien.ac.at/~lehrenfeld/xfem/exercise/ex2_twodom_poisson/twodom_poisson.pdf
    // The input file is in the "constructive solid geometry" format.
    std::string filename = "netgen_io.tmp";
    {
      std::ofstream netgen_io(filename.c_str());
      netgen_io << "algebraic3d\n";
      netgen_io << "solid left   = plane(-1, -1, -1; -1,  0,  0) -bc=1;\n";
      netgen_io << "solid front  = plane(-1, -1, -1;  0, -1,  0) -bc=3;\n";
      netgen_io << "solid bottom = plane(-1, -1, -1;  0,  0, -1) -bc=5;\n";
      netgen_io << "solid right  = plane( 1,  1,  1;  1,  0,  0) -bc=2;\n";
      netgen_io << "solid back   = plane( 1,  1,  1;  0,  1,  0) -bc=4;\n";
      netgen_io << "solid top    = plane( 1,  1,  1;  0,  0,  1) -bc=6;\n";
      netgen_io << "solid sph    = sphere(0, 0, 0; 0.5); -bc=7\n";
      netgen_io << "solid cube   = left and right and front and back and bottom and top;\n";
      // netgen_io << "solid inner  = cube and sph;\n"; // uncomment this line to fill sphere
      netgen_io << "solid outer  = cube and not sph;\n";
      netgen_io << "tlo outer -maxh=0.2;\n";
      // netgen_io << "tlo inner -maxh=0.15;\n"; // uncomment this line to fill sphere
    }

    // Stats for sphere-hole mesh
    // maxh=0.2, Points: 1172, Elements: 4665
    // maxh=0.1, Points: 9677, Elements: 48091
    // maxh=0.05, Points: 71264, Elements: 383019

    // Call the nglib interface to generate a Mesh from the geometry
    // described in the file.
    nglib::Ng_Mesh * netgen_mesh = NULL;
    nglib::Ng_Meshing_Parameters mp;
    nglib::Ng_Result res =
      nglib::Ng_CSG_GenerateMeshFromGeometryFile(filename.c_str(), &netgen_mesh, &mp);

    // Remove the temporary file now that we are done with it.
    std::remove(filename.c_str());

    // Build libmesh mesh to transfer points into
    Mesh mesh(init.comm(), 3);

    // Print lists of points and elements in volume mesh.
    {
      int np = nglib::Ng_GetNP(netgen_mesh);
      std::cout << "Points: " << np << std::endl;

      double point[3];
      for (int i = 1; i <= np; i++)
        {
          nglib::Ng_GetPoint (netgen_mesh, i, point);

          // Add points to libmesh mesh, use 1-based numbering like netgen.
          mesh.add_point(Point(point[0], point[1], point[2]), i);
        }

      int ne = nglib::Ng_GetNE(netgen_mesh);
      std::cout << "Elements: " << ne << std::endl;

      int tet[4];
      for (int i = 1; i <= ne; i++)
        {
          nglib::Ng_GetVolumeElement (netgen_mesh, i, tet);

          // Add tet to libmesh mesh, use 1-based numbering like
          // netgen.  Note that we have to swap the last two entries
          // of the connectivity array, because Netgen uses a
          // clockwise numbering for some reason.
          Elem* elem = mesh.add_elem(new Tet4);
          elem->set_node(0) = mesh.node_ptr(tet[0]);
          elem->set_node(1) = mesh.node_ptr(tet[1]);
          elem->set_node(2) = mesh.node_ptr(tet[3]);
          elem->set_node(3) = mesh.node_ptr(tet[2]);
        }
    }

    // Write mesh to Netgen-style file.
    nglib::Ng_SaveMesh(netgen_mesh, "cube_sphere.vol");

    // We're done with the Netgen mesh
    nglib::Ng_DeleteMesh(netgen_mesh);

    // We're now done calling Netgen functions
    nglib::Ng_Exit();

    // This is necessary, otherwise I get very strange results for
    // some reason (points with different coordinates than they are
    // supposed to have!
    mesh.prepare_for_use();

    // Write an Exodus file with the libmesh mesh
    mesh.write("netgen_test_04.e");
  }

  return 0;
}

Hi,
I try to use "Ng_CSG_GenerateMeshFromGeometryFile" but i find problems. Can you say me where is this definition?
Thanks
RP