Exemple #1
0
IGL_INLINE void igl::PolyVectorFieldFinder<DerivedV, DerivedF>::setFieldFromGeneralCoefficients(const  std::vector<Eigen::Matrix<std::complex<typename DerivedV::Scalar>, Eigen::Dynamic,1>> &coeffs,
                                                            std::vector<Eigen::Matrix<typename DerivedV::Scalar, Eigen::Dynamic, 2>> &pv)
{
  pv.assign(n, Eigen::Matrix<typename DerivedV::Scalar, Eigen::Dynamic, 2>::Zero(numF, 2));
  for (int i = 0; i <numF; ++i)
  {

    //    poly coefficients: 1, 0, -Acoeff, 0, Bcoeff
    //    matlab code from roots (given there are no trailing zeros in the polynomial coefficients)
    Eigen::Matrix<std::complex<typename DerivedV::Scalar>, Eigen::Dynamic,1> polyCoeff;
    polyCoeff.setZero(2*n+1,1);
    polyCoeff[0] = 1.;
    int sign = 1;
    for (int k =0; k<n; ++k)
    {
      sign = -sign;
      int degree = 2*(k+1);
      polyCoeff[degree] = (1.*sign)*coeffs[k](i);
    }

    Eigen::Matrix<std::complex<typename DerivedV::Scalar>, Eigen::Dynamic,1> roots;
    igl::polyRoots<std::complex<typename DerivedV::Scalar>, typename DerivedV::Scalar >(polyCoeff,roots);

    Eigen::VectorXi done; done.setZero(2*n,1);

    Eigen::Matrix<std::complex<typename DerivedV::Scalar>, Eigen::Dynamic,1> u(n,1);
    int ind =0;
    for (int k=0; k<2*n; ++k)
    {
      if (done[k])
        continue;
      u[ind] = roots[k];
      done[k] = 1;

      int mini = -1;
      double mind = 1e10;
      for (int l =k+1; l<2*n; ++l)
      {
        double dist = abs(roots[l]+u[ind]);
        if (dist<mind)
        {
          mind = dist;
          mini = l;
        }
      }
      done[mini] = 1;
      ind ++;
    }
    for (int k=0; k<n; ++k)
    {
      pv[k](i,0) = real(u[k]);
      pv[k](i,1) = imag(u[k]);
    }
  }

}
Exemple #2
0
IGL_INLINE void igl::PolyVectorFieldFinder<DerivedV, DerivedF>::
minQuadWithKnownMini(const Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar> > &Q,
                          const Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar> > &f,
                     const Eigen::VectorXi isConstrained,
                          const Eigen::Matrix<std::complex<typename DerivedV::Scalar>, Eigen::Dynamic, 1> &xknown,
                          Eigen::Matrix<std::complex<typename DerivedV::Scalar>, Eigen::Dynamic, 1> &x)
{
  int N = Q.rows();

  int nc = xknown.rows();
  Eigen::VectorXi known; known.setZero(nc,1);
  Eigen::VectorXi unknown; unknown.setZero(N-nc,1);

  int indk = 0, indu = 0;
  for (int i = 0; i<N; ++i)
    if (isConstrained[i])
    {
      known[indk] = i;
      indk++;
    }
    else
    {
      unknown[indu] = i;
      indu++;
    }

  Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar>> Quu, Quk;

  igl::slice(Q,unknown, unknown, Quu);
  igl::slice(Q,unknown, known, Quk);


  std::vector<typename Eigen::Triplet<std::complex<typename DerivedV::Scalar> > > tripletList;

  Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar> > fu(N-nc,1);

  igl::slice(f,unknown, Eigen::VectorXi::Zero(1,1), fu);

  Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar> > rhs = (Quk*xknown).sparseView()+.5*fu;

  Eigen::SparseLU< Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar>>> solver;
  solver.compute(-Quu);
  if(solver.info()!=Eigen::Success)
  {
    std::cerr<<"Decomposition failed!"<<std::endl;
    return;
  }
  Eigen::SparseMatrix<std::complex<typename DerivedV::Scalar>>  b  = solver.solve(rhs);
  if(solver.info()!=Eigen::Success)
  {
    std::cerr<<"Solving failed!"<<std::endl;
    return;
  }

  indk = 0, indu = 0;
  x.setZero(N,1);
  for (int i = 0; i<N; ++i)
    if (isConstrained[i])
      x[i] = xknown[indk++];
    else
      x[i] = b.coeff(indu++,0);

}
Exemple #3
0
void
pcl::Permutohedral::init (const std::vector<float> &feature, const int feature_dimension, const int N)
{
  N_ = N;
  d_ = feature_dimension;
  
  // Create hash table
  std::vector<std::vector<short> > keys;
  keys.reserve ((d_+1) * N_);
  std::multimap<size_t, int> hash_table;

  // reserve class memory
  if (offset_.size () > 0) 
    offset_.clear ();
  offset_.resize ((d_ + 1) * N_);

  if (barycentric_.size () > 0) 
    barycentric_.clear ();
  barycentric_.resize ((d_ + 1) * N_);

  // create vectors and matrices
  Eigen::VectorXf scale_factor = Eigen::VectorXf::Zero (d_);
  Eigen::VectorXf elevated = Eigen::VectorXf::Zero (d_ + 1);
  Eigen::VectorXf rem0 = Eigen::VectorXf::Zero (d_+1);
  Eigen::VectorXf barycentric = Eigen::VectorXf::Zero (d_+2);
  Eigen::VectorXi rank = Eigen::VectorXi::Zero (d_+1);
  Eigen::Matrix<int, Eigen::Dynamic, Eigen::Dynamic> canonical;
  canonical = Eigen::Matrix<int, Eigen::Dynamic, Eigen::Dynamic>::Zero (d_+1, d_+1);
  //short * key = new short[d_+1];
  std::vector<short> key (d_+1);

  // Compute the canonical simple
  for (int i = 0; i <= d_; i++)
  {
    for (int j = 0; j <= (d_ - i); j++)
      canonical (j, i) = i;
    for (int j = (d_ - i + 1); j <= d_; j++)
      canonical (j, i) = i - (d_ + 1);
  }

  // Expected standard deviation of our filter (p.6 in [Adams etal 2010])
  float inv_std_dev = std::sqrt (2.0f / 3.0f) * static_cast<float> (d_ + 1);
  
  // Compute the diagonal part of E (p.5 in [Adams etal 2010])
  for (int i = 0; i < d_; i++)
    scale_factor (i) = 1.0f / std::sqrt (static_cast<float> (i + 2) * static_cast<float> (i + 1)) * inv_std_dev;

  // Compute the simplex each feature lies in
  for (int k = 0; k < N_; k++)
    //for (int k = 0; k < 5; k++)
  {

    // Elevate the feature  (y = Ep, see p.5 in [Adams etal 2010])
    int index = k * feature_dimension;
    // sm contains the sum of 1..n of our faeture vector
    float sm = 0;
    for (int j = d_; j > 0; j--)
    {
      float cf = feature[index + j-1] * scale_factor (j-1);      
      elevated (j) = sm - static_cast<float> (j) * cf;
      sm += cf;
    }
    elevated (0) = sm;

    // Find the closest 0-colored simplex through rounding
    float down_factor = 1.0f / static_cast<float>(d_+1);
    float up_factor = static_cast<float>(d_+1);
    int sum = 0;
    for (int j = 0; j <= d_; j++){
      float rd = floorf (0.5f + (down_factor * elevated (j))) ;
      rem0 (j) = rd * up_factor;
      sum += static_cast<int> (rd);
    }
    
    // rank differential to find the permutation between this simplex and the canonical one.         
    // (See pg. 3-4 in paper.)    
    rank.setZero ();
    Eigen::VectorXf tmp = elevated - rem0;
    for (int i = 0; i < d_; i++){
      for (int j = i+1; j <= d_; j++)
        if (tmp (i) < tmp (j))
          rank (i)++;
        else
          rank (j)++;
    }

    // If the point doesn't lie on the plane (sum != 0) bring it back
    for (int j = 0; j <= d_; j++){
      rank (j) += sum;
      if (rank (j) < 0){
        rank (j) += d_+1;
        rem0 (j) += static_cast<float> (d_ + 1);
      }
      else if (rank (j) > d_){
        rank (j) -= d_+1;
        rem0 (j) -= static_cast<float> (d_ + 1);
      }
    }

    // Compute the barycentric coordinates (p.10 in [Adams etal 2010])
    barycentric.setZero ();
    Eigen::VectorXf v = (elevated - rem0) * down_factor;
    for (int j = 0; j <= d_; j++){
      barycentric (d_ - rank (j)    ) += v (j);
      barycentric (d_ + 1 - rank (j)) -= v (j);
    }
    // Wrap around
    barycentric (0) += 1.0f + barycentric (d_+1);

    // Compute all vertices and their offset
    for (int remainder = 0; remainder <= d_; remainder++)
    {
      for (int j = 0; j < d_; j++)
        key[j] = static_cast<short> (rem0 (j) + static_cast<float> (canonical ( rank (j), remainder)));

      // insert key in hash table      
      size_t hash_key = generateHashKey (key);
      auto it = hash_table.find (hash_key);
      int key_index = -1;
      if (it != hash_table.end ())
      {
        key_index = it->second;
        
        // check if key is the right one
        int tmp_key_index = -1;
        //for (int ii = key_index; ii < keys.size (); ii++)
        for (; it != hash_table.end (); ++it)
        {
          int ii = it->second;
          bool same = true;
          std::vector<short> k = keys[ii];
          for (size_t i_k = 0; i_k < k.size (); i_k++)
          {
            if (key[i_k] != k[i_k])
            {
              same = false;
              break;
            }
          }

          if (same)
          {
            tmp_key_index = ii;
            break;
          }
        }
      
        if (tmp_key_index == -1)
        {
          key_index = static_cast<int> (keys.size ());
          keys.push_back (key);
          hash_table.insert (std::pair<size_t, int> (hash_key, key_index));
        }
        else
          key_index = tmp_key_index;
      }
      
      else
      {  
        key_index = static_cast<int> (keys.size ());
        keys.push_back (key);
        hash_table.insert (std::pair<size_t, int> (hash_key, key_index));
      }
      offset_[ k * (d_ + 1) + remainder ] = static_cast<float> (key_index);
      
      barycentric_[ k * (d_ + 1) + remainder ] = barycentric (remainder);
    }
  }

  // Find the Neighbors of each lattice point
		
  // Get the number of vertices in the lattice
  M_ = static_cast<int> (hash_table.size());
		
  // Create the neighborhood structure
  if (blur_neighbors_.size () > 0) 
    blur_neighbors_.clear ();
  blur_neighbors_.resize ((d_+1)*M_);

  std::vector<short> n1 (d_+1);
  std::vector<short> n2 (d_+1);

  // For each of d+1 axes,
  for (int j = 0; j <= d_; j++)
  {
    for (int i = 0; i < M_; i++)
    {
      std::vector<short> key = keys[i];

      for (int k=0; k<d_; k++){
        n1[k] = static_cast<short> (key[k] - 1);
        n2[k] = static_cast<short> (key[k] + 1);
      }
      n1[j] = static_cast<short> (key[j] + d_);
      n2[j] = static_cast<short> (key[j] - d_);

      std::multimap<size_t ,int>::iterator it;
      size_t hash_key;
      int key_index = -1;      
      hash_key = generateHashKey (n1);
      it = hash_table.find (hash_key);
      if (it != hash_table.end ())
        key_index = it->second;
      blur_neighbors_[j*M_+i].n1 = key_index;

      key_index = -1;
      hash_key = generateHashKey (n2);
      it = hash_table.find (hash_key);
      if (it != hash_table.end ())
        key_index = it->second;
      blur_neighbors_[j*M_+i].n2 = key_index;
    }
  }
}
IGL_INLINE void igl::parallel_transport_angles(
const Eigen::PlainObjectBase<DerivedV>& V,
const Eigen::PlainObjectBase<DerivedF>& F,
const Eigen::PlainObjectBase<DerivedV>& FN,
const Eigen::MatrixXi &E2F,
const Eigen::MatrixXi &F2E,
Eigen::PlainObjectBase<DerivedK> &K)
{
  int numE = E2F.rows();

  Eigen::VectorXi isBorderEdge;
  isBorderEdge.setZero(numE,1);
  for(unsigned i=0; i<numE; ++i)
  {
    if ((E2F(i,0) == -1) || ((E2F(i,1) == -1)))
      isBorderEdge[i] = 1;
  }

  K.setZero(numE);
  // For every non-border edge
  for (unsigned eid=0; eid<numE; ++eid)
  {
    if (!isBorderEdge[eid])
    {
      int fid0 = E2F(eid,0);
      int fid1 = E2F(eid,1);

      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> N0 = FN.row(fid0);
//      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> N1 = FN.row(fid1);

      // find common edge on triangle 0 and 1
      int fid0_vc = -1;
      int fid1_vc = -1;
      for (unsigned i=0;i<3;++i)
      {
        if (F2E(fid0,i) == eid)
          fid0_vc = i;
        if (F2E(fid1,i) == eid)
          fid1_vc = i;
      }
      assert(fid0_vc != -1);
      assert(fid1_vc != -1);

      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> common_edge = V.row(F(fid0,(fid0_vc+1)%3)) - V.row(F(fid0,fid0_vc));
      common_edge.normalize();

      // Map the two triangles in a new space where the common edge is the x axis and the N0 the z axis
      Eigen::Matrix<typename DerivedV::Scalar, 3, 3> P;
      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> o = V.row(F(fid0,fid0_vc));
      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> tmp = -N0.cross(common_edge);
      P << common_edge, tmp, N0;
      //      P.transposeInPlace();


      Eigen::Matrix<typename DerivedV::Scalar, 3, 3> V0;
      V0.row(0) = V.row(F(fid0,0)) -o;
      V0.row(1) = V.row(F(fid0,1)) -o;
      V0.row(2) = V.row(F(fid0,2)) -o;

      V0 = (P*V0.transpose()).transpose();

      //      assert(V0(0,2) < 1e-10);
      //      assert(V0(1,2) < 1e-10);
      //      assert(V0(2,2) < 1e-10);

      Eigen::Matrix<typename DerivedV::Scalar, 3, 3> V1;
      V1.row(0) = V.row(F(fid1,0)) -o;
      V1.row(1) = V.row(F(fid1,1)) -o;
      V1.row(2) = V.row(F(fid1,2)) -o;
      V1 = (P*V1.transpose()).transpose();

      //      assert(V1(fid1_vc,2) < 10e-10);
      //      assert(V1((fid1_vc+1)%3,2) < 10e-10);

      // compute rotation R such that R * N1 = N0
      // i.e. map both triangles to the same plane
      double alpha = -atan2(V1((fid1_vc+2)%3,2),V1((fid1_vc+2)%3,1));

      Eigen::Matrix<typename DerivedV::Scalar, 3, 3> R;
      R << 1,          0,            0,
      0, cos(alpha), -sin(alpha) ,
      0, sin(alpha),  cos(alpha);
      V1 = (R*V1.transpose()).transpose();

      //      assert(V1(0,2) < 1e-10);
      //      assert(V1(1,2) < 1e-10);
      //      assert(V1(2,2) < 1e-10);

      // measure the angle between the reference frames
      // k_ij is the angle between the triangle on the left and the one on the right
      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> ref0 = V0.row(1) - V0.row(0);
      Eigen::Matrix<typename DerivedV::Scalar, 1, 3> ref1 = V1.row(1) - V1.row(0);

      ref0.normalize();
      ref1.normalize();

      double ktemp = atan2(ref1(1),ref1(0)) - atan2(ref0(1),ref0(0));

      // just to be sure, rotate ref0 using angle ktemp...
      Eigen::Matrix<typename DerivedV::Scalar,2,2> R2;
      R2 << cos(ktemp), -sin(ktemp), sin(ktemp), cos(ktemp);

//      Eigen::Matrix<typename DerivedV::Scalar, 1, 2> tmp1 = R2*(ref0.head(2)).transpose();

      //      assert(tmp1(0) - ref1(0) < 1e-10);
      //      assert(tmp1(1) - ref1(1) < 1e-10);

      K[eid] = ktemp;
    }
  }

}
Exemple #5
0
// A tet is organized in the following fashion:
//
//       0
//       
//       3       (3 is in the background; 1 and 2 are in the foreground)
//  2        1
//
// So the faces (with counterclockwise normals) are:
// (0 1 3)
// (0 2 1)
// (3 2 0)
// (1 2 3)
//
//
// This method will perform three steps:
// 1. Add all faces, duplicating ones on the interior
// 2. Remove all duplicate verts (might have been caused during #1)
// 3. Remove all duplicate faces
void marching_tets(
  const Eigen::MatrixXd& V,
  const Eigen::MatrixXi& T,
  const Eigen::VectorXd& H,
  double offset,
  Eigen::MatrixXd& NV,
  Eigen::MatrixXi& NF,
  Eigen::VectorXi& I)
{
  min_how_much = 1;
  max_how_much = 0;
  using namespace Eigen;
  using namespace std;

  // Count the faces.
  std::map<std::vector<int>, int> face_counts;
  for (int i = 0; i < T.rows(); ++i) {
    std::vector<std::vector<int> > fs;
    fs.push_back({T(i, 0), T(i, 1), T(i, 3)});
    fs.push_back({T(i, 0), T(i, 2), T(i, 1)});
    fs.push_back({T(i, 3), T(i, 2), T(i, 0)});
    fs.push_back({T(i, 1), T(i, 2), T(i, 3)});
    for (auto &f : fs) {
      std::sort(f.begin(), f.end());
      // Add it to the map.
      face_counts[f]++;
    }
  }

  vector<Eigen::RowVector3i> faces;
  vector<int> faces_markers;
  vector<Eigen::RowVector3d> new_verts;
  int times[6];
  for (int i = 0; i < 6; i++) {
    times[i] = 0;
  }

  // Create data structure.
  MarchingTetsDat dd(V, H, faces, faces_markers, face_counts, new_verts, offset);

  int numEq = 0;

  // Check each tet face, add as needed.
  for (int i = 0; i < T.rows(); ++i) {
    // See if the tet is entirely inside.
    vector<int> inside, outside, inside_t, outside_t, identical;
    for (int j = 0; j < T.cols(); ++j) {
      //if (H(T(i, j)) > offset + 1e-4) {
      if (H(T(i, j)) > offset) {
        outside.push_back(j);
      } else if (H(T(i, j)) < offset) {
        inside.push_back(j);
      } else {
        numEq++;
        identical.push_back(j);
      }

      if (H(T(i, j)) == GLOBAL::outside_temp) {
        outside_t.push_back(j);
      } else if (H(T(i, j)) == GLOBAL::inside_temp) {
        inside_t.push_back(j);
      }
    }

    // Ignore this tet if it's entirely outside.
    if (outside.size() == 4) {
      continue;
    }


    if (outside.size() == 0 && inside.size() == 0) {
      // degenerate, ignore.
      printf("WARNING: degenerate tet face found!!\n");
    } else if (inside.size() == 0 && identical.size() < 3) {
      // Nothing to add.
    } else if (identical.size() == 3) {
      //addOrig(T.row(i), 7, dd.faces, dd.faces_markers);
      // Ignore it if there's only one on the outside.
      //if (inside.size() == 0) continue;
      if (outside.size() == 0) continue;
      times[1]++;
      // Add just a single face (always)
      int i1 = T(i,identical[0]), i2 = T(i,identical[1]), i3 = T(i,identical[2]);
      Eigen::RowVector3i f({i1, i2, i3});
      dd.faces.push_back(f);
      dd.faces_markers.push_back(1);
    } else if (outside.size() == 0) {
      // (these are colored blue)
      times[0]++;
      // (A) Takes care of:
      //   inside: 1, identical: 3 (remove three duplicated faces later)
      //   inside: 2, identical: 2 (remove all four duplicated faces later)
      //   inside: 3, identical: 1 (remove all four duplicated faces later)
      //   inside: 4, identical: 0 (remove all four duplicated faces later)
      case0Out(dd, T.row(i), inside, outside, identical, inside_t, outside_t);
    } else if (inside.size() == 1) {
      // (these are colored green)
      times[2]++;
      // (B) Takes care of:
      //   inside: 1 outside: 3
      //   inside: 1 outside: 2 identical: 1
      //   inside: 1 outside: 1 identical: 2
      //
      case1In(dd, T.row(i), inside, outside, identical, inside_t, outside_t);
    } else if (inside.size() == 3 && outside.size() == 1) {
      // (these are colored orange)
      times[3]++;
      // (C) takes care of:
      //   inside: 3 outside: 1
      //
      case3In1Out(dd, T.row(i), inside, outside, identical, inside_t, outside_t);
    } else if (inside.size() == 2 && outside.size() >= 1) {
      // (these are colored red)
      times[4]++;
      // (D) takes care of:
      //   inside: 2 outside: 1 identical: 1
      //   inside: 2 outside: 2 identical: 0
      //
      case2In2Out(dd, T.row(i), inside, outside, identical, inside_t, outside_t);
    } else {
      times[5]++;
      fprintf(stderr, "WARN: marching tets found something weird, with in:%lu out:%lu\n",
              inside.size(), outside.size());
    }
  }

  printf("Finished marching tets with usages:\n");
  for (int i = 0; i < 6; ++i) {
    printf("  %d: %d\n", i, times[i]);
  }
  printf("how_much is %lf and EPS is %lf\n", min_how_much, GLOBAL::EPS);
  printf("     max is %lf\n", max_how_much);
  printf("Num equal is %d\n", numEq);

  // Copy verts
  NV.resize(V.rows() + new_verts.size(), 3);
  for (int i = 0; i < V.rows(); ++i) {
    NV.row(i) = V.row(i);
  }
  for (int i = 0; i < new_verts.size(); ++i) {
    NV.row(i + V.rows()) = new_verts[i];
  }
  // Set I
  I.resize(NV.rows());
  for (int i = 0; i < I.rows(); ++i) {
    if (i < V.rows()) {
      I(i) = i;
    } else {
      I(i) = -1;
    }
  }
  Eigen::VectorXi facesMarkers;
  facesMarkers.resize(faces.size());
  // Copy faces
  NF.resize(faces.size(), 3);
  for (int i = 0; i < faces.size(); ++i) {
    NF.row(i) = faces[i];
    facesMarkers(i) = faces_markers[i];
  }
  
  Eigen::MatrixXd newV;
  Eigen::MatrixXi newF;
  Eigen::VectorXi SVJ, SVI, I2;
  // Helpers::viewTriMesh(NV, NF, facesMarkers);
  //igl::writeOFF("offset_mesh.off", NV, NF)
  Helpers::writeMeshWithMarkers("offset_mesh", NV, NF, facesMarkers);

  /*
  igl::collapse_small_triangles(NV, NF, 1e-8, newF);
  printf("Collapsed %d small triangles\n", NF.rows() - newF.rows());
  NF = newF;
  */

  ///*
  igl::remove_duplicate_vertices(NV, NF, 1e-20, newV, SVI, SVJ, newF);
  I2.resize(newV.rows());
  I2.setConstant(-1);
  for (int i = 0; i < NV.rows(); ++i) {
    if (I2(SVJ(i)) == -1) {
      I2(SVJ(i)) = I(i);
    } else {
      I2(SVJ(i)) = std::min(I2(SVJ(i)), I(i));
    }
  }
  NF = newF;
  NV = newV;
  I = I2;

  // Now see if we have duplicated faces.
  //igl::resolve_duplicated_faces(NF, newF, SVJ);
  //NF = newF;
  //*/

  // Other option is to do these two:
  // These are bad because sometimes the "small" triangles are not area zero,
  // and doing the removeDuplicates will delete these triangles and make the
  // mesh non-manifold. Better to wait for remeshing later.
  //Helpers::removeDuplicates(NV, NF, I);
  //Helpers::collapseSmallTriangles(NV, NF);

  igl::remove_unreferenced(NV, NF, newV, newF, SVI, SVJ);
  I2.resize(newV.rows());
  I2.setConstant(-1);
  for (int i = 0; i < I2.rows(); ++i) {
    I2(i) = I(SVJ(i));
  }
  I = I2;
  NV = newV;
  NF = newF;


  // orient everything correctly.
  Eigen::VectorXi C;
  igl::orientable_patches(NF, C);
  igl::bfs_orient(NF, newF, C);
  NF = newF;
  igl::orient_outward(NV, NF, C, newF, SVJ);
  NF = newF;
  //igl::writeOFF("offset_mesh_normals.off", NV, NF);

#ifdef DEBUG_MESH
  if (!Helpers::isMeshOkay(NV, NF)) {
    printf("Error: Mesh is not okay at first...\n");
  }
  if (!Helpers::isManifold(NV, NF, I)) {
    printf("Error: Mesh from marching tets not manifold!\n");
    Eigen::VectorXi temp;
    temp.resize(I.rows());
    temp.setZero();
    Helpers::isManifold(NV, NF, temp, true);
    Helpers::viewTriMesh(NV, NF, temp);
    Helpers::writeMeshWithMarkers("marching_tets_manifold", NV, NF, temp);
    cout << "See marching_tets_manifold.off for problems.\n";
    exit(1);
  }
#endif
}