libigl_Martin/python/203_CurvatureDirections.py

import igl





  std::string filename = "../shared/fertility.off";
  if(argc>1)
  {
    filename = argv[1];
  }
  // Load a mesh in OFF format
  igl::read_triangle_mesh(filename, V, F);

  // Alternative discrete mean curvature
  MatrixXd HN;
  SparseMatrix<double> L,M,Minv;
  igl::cotmatrix(V,F,L);
  igl::massmatrix(V,F,igl::MASSMATRIX_TYPE_VORONOI,M);
  igl::invert_diag(M,Minv);
  // Laplace-Beltrami of position
  HN = -Minv*(L*V);
  // Extract magnitude as mean curvature
  VectorXd H = HN.rowwise().norm();

  // Compute curvature directions via quadric fitting
  MatrixXd PD1,PD2;
  VectorXd PV1,PV2;
  igl::principal_curvature(V,F,PD1,PD2,PV1,PV2);
  // mean curvature
  H = 0.5*(PV1+PV2);

  igl::viewer::Viewer viewer;
  viewer.data.set_mesh(V, F);


  // Compute pseudocolor
  MatrixXd C;
  igl::parula(H,true,C);
  viewer.data.set_colors(C);

  // Average edge length for sizing
  const double avg = igl::avg_edge_length(V,F);

  // Draw a blue segment parallel to the minimal curvature direction
  const RowVector3d red(0.8,0.2,0.2),blue(0.2,0.2,0.8);
  viewer.data.add_edges(V + PD1*avg, V - PD1*avg, blue);

  // Draw a red segment parallel to the maximal curvature direction
  viewer.data.add_edges(V + PD2*avg, V - PD2*avg, red);

  // Hide wireframe
  viewer.core.show_lines = false;

  viewer.launch();
}