TetGenInterface.cpp

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#include "TetGenInterface.h"
 
#include <cstddef>
#include <fstream>
#include <string>
 
#include "BaseLib/FileTools.h"
#include "BaseLib/Logging.h"
#include "BaseLib/StringTools.h"
#include "GeoLib/Triangle.h"
#include "MeshLib/Elements/Element.h"
#include "MeshLib/Elements/Tet.h"
#include "MeshLib/Mesh.h"
#include "MeshLib/MeshInformation.h"
#include "MeshLib/Node.h"
 
namespace FileIO
{
TetGenInterface::TetGenInterface() = default;
 
bool TetGenInterface::readTetGenGeometry(std::string const& geo_fname,
                                         GeoLib::GEOObjects& geo_objects)
{
    std::ifstream poly_stream(geo_fname.c_str());
 
    if (!poly_stream)
    {
        ERR("TetGenInterface::readTetGenGeometry() failed to open {:s}",
            geo_fname);
        return false;
    }
    std::string ext(BaseLib::getFileExtension(geo_fname));
    if (ext != ".smesh")
    {
        ERR("TetGenInterface::readTetGenGeometry() - unknown file type (only "
            "*.smesh is supported).");
        return false;
    }
 
    std::vector<MeshLib::Node*> nodes;
    if (!readNodesFromStream(poly_stream, nodes))
    {
        // remove nodes read until now
        for (auto& node : nodes)
        {
            delete node;
        }
        return false;
    }
    const std::size_t nNodes(nodes.size());
    auto points = std::make_unique<std::vector<GeoLib::Point*>>();
    points->reserve(nNodes);
    for (std::size_t k(0); k < nNodes; ++k)
    {
        points->push_back(new GeoLib::Point(*(nodes[k]), nodes[k]->getID()));
        delete nodes[k];
    }
    std::string geo_name(BaseLib::extractBaseNameWithoutExtension(geo_fname));
    geo_objects.addPointVec(std::move(points), geo_name);
    const std::vector<std::size_t>& id_map(
        geo_objects.getPointVecObj(geo_name)->getIDMap());
 
    auto surfaces = std::make_unique<std::vector<GeoLib::Surface*>>();
    if (!parseSmeshFacets(
            poly_stream, *surfaces, *geo_objects.getPointVec(geo_name), id_map))
    {
        // remove surfaces read until now but keep the points
        for (std::size_t k = 0; k < surfaces->size(); k++)
        {
            delete (*surfaces)[k];
        }
    }
    geo_objects.addSurfaceVec(std::move(surfaces), geo_name);
 
    return true;
}
 
std::size_t TetGenInterface::getNFacets(std::ifstream& input)
{
    std::string line;
    while (!input.fail())
    {
        getline(input, line);
        if (input.fail())
        {
            ERR("TetGenInterface::getNFacets(): Error reading number of "
                "facets.");
            return 0;
        }
 
        BaseLib::simplify(line);
        if (line.empty() || line.compare(0, 1, "#") == 0)
        {
            continue;
        }
 
        const std::list<std::string> fields = BaseLib::splitString(line, ' ');
        auto it = fields.begin();
        const auto nFacets(BaseLib::str2number<std::size_t>(*it));
        if (fields.size() > 1)
        {
            _boundary_markers = BaseLib::str2number<std::size_t>(*(++it)) != 0;
        }
        return nFacets;
    }
    return 0;
}
 
bool TetGenInterface::parseSmeshFacets(
    std::ifstream& input,
    std::vector<GeoLib::Surface*>& surfaces,
    const std::vector<GeoLib::Point*>& points,
    const std::vector<std::size_t>& pnt_id_map)
{
    const std::size_t nFacets(this->getNFacets(input));
    std::string line;
    surfaces.reserve(nFacets);
    std::list<std::string>::const_iterator it;
 
    const unsigned offset = (_zero_based_idx) ? 0 : 1;
    std::vector<std::size_t> idx_map;
 
    std::size_t k(0);
    while (k < nFacets && !input.fail())
    {
        getline(input, line);
        if (input.fail())
        {
            ERR("TetGenInterface::parseFacets(): Error reading facet {:d}.", k);
            return false;
        }
 
        BaseLib::simplify(line);
        if (line.empty() || line.compare(0, 1, "#") == 0)
        {
            continue;
        }
 
        // read facets
        const std::list<std::string> point_fields =
            BaseLib::splitString(line, ' ');
        it = point_fields.begin();
        const auto nPoints = BaseLib::str2number<std::size_t>(*it);
        if (nPoints != 3)
        {
            ERR("Smesh-files are currently only supported for triangle "
                "meshes.");
            return false;
        }
        std::vector<std::size_t> point_ids;
        const std::size_t point_field_size =
            (_boundary_markers) ? nPoints + 1 : nPoints;
        if (point_fields.size() > point_field_size)
        {
            for (std::size_t j(0); j < nPoints; ++j)
            {
                point_ids.push_back(
                    pnt_id_map[BaseLib::str2number<std::size_t>(*(++it)) -
                               offset]);
            }
 
            const std::size_t sfc_marker =
                (_boundary_markers) ? BaseLib::str2number<std::size_t>(*(++it))
                                    : 0;
            const std::size_t idx =
                std::find(idx_map.begin(), idx_map.end(), sfc_marker) -
                idx_map.begin();
            if (idx >= surfaces.size())
            {
                idx_map.push_back(sfc_marker);
                surfaces.push_back(new GeoLib::Surface(points));
            }
            surfaces[idx]->addTriangle(
                point_ids[0], point_ids[1], point_ids[2]);
        }
        else
        {
            ERR("TetGenInterface::parseFacets(): Error reading points for "
                "facet {:d}.",
                k);
            return false;
        }
        ++k;
    }
    // here the poly-file potentially defines a number of points to mark holes
    // within the volumes defined by the facets, these are ignored for now here
    // the poly-file potentially defines a number of region attributes, these
    // are ignored for now
 
    std::size_t nTotalTriangles(0);
    for (auto& surface : surfaces)
    {
        nTotalTriangles += surface->getNumberOfTriangles();
    }
    if (nTotalTriangles == nFacets)
    {
        return true;
    }
 
    ERR("TetGenInterface::parseFacets(): Number of expected total triangles "
        "({:d}) does not match number of found triangles ({:d}).",
        surfaces.size(),
        nTotalTriangles);
    return false;
}
 
MeshLib::Mesh* TetGenInterface::readTetGenMesh(std::string const& nodes_fname,
                                               std::string const& ele_fname)
{
    std::ifstream ins_nodes(nodes_fname.c_str());
    std::ifstream ins_ele(ele_fname.c_str());
 
    if (!ins_nodes || !ins_ele)
    {
        if (!ins_nodes)
        {
            ERR("TetGenInterface::readTetGenMesh failed to open {:s}",
                nodes_fname);
        }
        if (!ins_ele)
        {
            ERR("TetGenInterface::readTetGenMesh failed to open {:s}",
                ele_fname);
        }
        return nullptr;
    }
 
    std::vector<MeshLib::Node*> nodes;
    if (!readNodesFromStream(ins_nodes, nodes))
    {
        // remove nodes read until now
        for (auto& node : nodes)
        {
            delete node;
        }
        return nullptr;
    }
 
    std::vector<MeshLib::Element*> elements;
    std::vector<int> materials;
    if (!readElementsFromStream(ins_ele, elements, materials, nodes))
    {
        BaseLib::cleanupVectorElements(nodes, elements);
        return nullptr;
    }
 
    MeshLib::Properties properties;
    // Transmit material values if there is any material value != 0
    if (std::any_of(
            materials.cbegin(), materials.cend(), [](int m) { return m != 0; }))
    {
        auto* const mat_props = properties.createNewPropertyVector<int>(
            "MaterialIDs", MeshLib::MeshItemType::Cell);
        mat_props->reserve(elements.size());
        std::copy(materials.cbegin(),
                  materials.cend(),
                  std::back_inserter(*mat_props));
    }
 
    const std::string mesh_name(
        BaseLib::extractBaseNameWithoutExtension(nodes_fname));
    return new MeshLib::Mesh(mesh_name, nodes, elements, properties);
}
 
bool TetGenInterface::readNodesFromStream(std::ifstream& ins,
                                          std::vector<MeshLib::Node*>& nodes)
{
    std::string line;
    getline(ins, line);
    std::size_t n_nodes;
    std::size_t dim;
    std::size_t n_attributes;
    bool boundary_markers;
 
    while (!ins.fail())
    {
        BaseLib::simplify(line);
        if (line.empty() || line.compare(0, 1, "#") == 0)
        {
            // this line is a comment - skip
            getline(ins, line);
            continue;
        }
        // read header line
        bool header_okay = parseNodesFileHeader(
            line, n_nodes, dim, n_attributes, boundary_markers);
        if (!header_okay)
        {
            return false;
        }
        if (!parseNodes(ins, nodes, n_nodes, dim))
        {
            return false;
        }
        return true;
    }
    return false;
}
 
bool TetGenInterface::parseNodesFileHeader(std::string const& line,
                                           std::size_t& n_nodes,
                                           std::size_t& dim,
                                           std::size_t& n_attributes,
                                           bool& boundary_markers)
{
    std::list<std::string> pnt_header = BaseLib::splitString(line, ' ');
    if (pnt_header.empty())
    {
        ERR("TetGenInterface::parseNodesFileHeader(): could not read number of "
            "nodes specified in header.");
        return false;
    }
    auto it = pnt_header.begin();
    n_nodes = BaseLib::str2number<std::size_t>(*it);
    dim = (pnt_header.size() == 1) ? 3
                                   : BaseLib::str2number<std::size_t>(*(++it));
 
    if (pnt_header.size() < 4)
    {
        n_attributes = 0;
        boundary_markers = false;
        return true;
    }
 
    n_attributes = BaseLib::str2number<std::size_t>(*(++it));
    boundary_markers = *(++it) == "1";
 
    return true;
}
 
bool TetGenInterface::parseNodes(std::ifstream& ins,
                                 std::vector<MeshLib::Node*>& nodes,
                                 std::size_t n_nodes,
                                 std::size_t dim)
{
    std::string line;
    nodes.reserve(n_nodes);
 
    std::size_t k(0);
    while (k < n_nodes && !ins.fail())
    {
        std::vector<double> coordinates(dim);
        std::getline(ins, line);
        if (ins.fail())
        {
            ERR("TetGenInterface::parseNodes(): Error reading node {:d}.", k);
            return false;
        }
 
        std::size_t id;
        std::size_t pos_end = 0;
        std::size_t pos_beg = line.find_first_not_of(' ', pos_end);
        pos_end = line.find_first_of(" \n", pos_beg);
 
        if (line.empty() || pos_beg == pos_end ||
            line.compare(pos_beg, 1, "#") == 0)
        {
            continue;
        }
 
        if (pos_beg != std::string::npos && pos_end != std::string::npos)
        {
            id = BaseLib::str2number<std::size_t>(
                line.substr(pos_beg, pos_end - pos_beg));
            if (k == 0 && id == 0)
            {
                _zero_based_idx = true;
            }
        }
        else
        {
            ERR("TetGenInterface::parseNodes(): Error reading ID of node {:d}.",
                k);
            return false;
        }
        // read coordinates
        const unsigned offset = (_zero_based_idx) ? 0 : 1;
        for (std::size_t i(0); i < dim; i++)
        {
            pos_beg = line.find_first_not_of(' ', pos_end);
            pos_end = line.find_first_of(" \n", pos_beg);
            if (pos_end == std::string::npos)
            {
                pos_end = line.size();
            }
            if (pos_beg != std::string::npos)
            {
                coordinates[i] = BaseLib::str2number<double>(
                    line.substr(pos_beg, pos_end - pos_beg));
            }
            else
            {
                ERR("TetGenInterface::parseNodes(): error reading coordinate "
                    "{:d} of node {:d}.",
                    i,
                    k);
                return false;
            }
        }
 
        nodes.push_back(new MeshLib::Node(coordinates.data(), id - offset));
        // read attributes and boundary markers ... - at the moment we do not
        // use this information
        ++k;
    }
 
    return true;
}
 
bool TetGenInterface::readElementsFromStream(
    std::ifstream& ins,
    std::vector<MeshLib::Element*>& elements,
    std::vector<int>& materials,
    const std::vector<MeshLib::Node*>& nodes) const
{
    std::string line;
    std::getline(ins, line);
    std::size_t n_tets;
    std::size_t n_nodes_per_tet;
    bool region_attributes;
 
    while (!ins.fail())
    {
        BaseLib::simplify(line);
        if (line.empty() || line.compare(0, 1, "#") == 0)
        {
            // this line is a comment - skip
            std::getline(ins, line);
            continue;
        }
 
        // read header line
        bool header_okay = parseElementsFileHeader(
            line, n_tets, n_nodes_per_tet, region_attributes);
        if (!header_okay)
        {
            return false;
        }
        if (!parseElements(ins,
                           elements,
                           materials,
                           nodes,
                           n_tets,
                           n_nodes_per_tet,
                           region_attributes))
        {
            return false;
        }
        return true;
    }
    return false;
}
 
bool TetGenInterface::parseElementsFileHeader(std::string& line,
                                              std::size_t& n_tets,
                                              std::size_t& n_nodes_per_tet,
                                              bool& region_attribute)
{
    std::size_t pos_beg;
    std::size_t pos_end;
 
    // number of tetrahedras
    pos_beg = line.find_first_not_of(' ');
    pos_end = line.find_first_of(' ', pos_beg);
    if (pos_beg != std::string::npos && pos_end != std::string::npos)
    {
        n_tets = BaseLib::str2number<std::size_t>(
            line.substr(pos_beg, pos_end - pos_beg));
    }
    else
    {
        ERR("TetGenInterface::parseElementsFileHeader(): Could not read number "
            "of tetrahedra specified in header.");
        return false;
    }
    // nodes per tet - either 4 or 10
    pos_beg = line.find_first_not_of(" \t", pos_end);
    pos_end = line.find_first_of(" \t", pos_beg);
    n_nodes_per_tet = BaseLib::str2number<std::size_t>(
        line.substr(pos_beg, pos_end - pos_beg));
    // region attribute at tetrahedra?
    pos_beg = line.find_first_not_of(" \t", pos_end);
    pos_end = line.find_first_of(" \t\n", pos_beg);
    if (pos_end == std::string::npos)
    {
        pos_end = line.size();
    }
    region_attribute = line.substr(pos_beg, pos_end - pos_beg) == "1";
 
    return true;
}
 
bool TetGenInterface::parseElements(std::ifstream& ins,
                                    std::vector<MeshLib::Element*>& elements,
                                    std::vector<int>& materials,
                                    const std::vector<MeshLib::Node*>& nodes,
                                    std::size_t n_tets,
                                    std::size_t n_nodes_per_tet,
                                    bool region_attribute) const
{
    std::string line;
    std::vector<std::size_t> ids(n_nodes_per_tet);
 
    elements.reserve(n_tets);
    materials.reserve(n_tets);
 
    const unsigned offset = (_zero_based_idx) ? 0 : 1;
    for (std::size_t k(0); k < n_tets && !ins.fail(); k++)
    {
        getline(ins, line);
        if (ins.fail())
        {
            ERR("TetGenInterface::parseElements(): Error reading tetrahedron "
                "{:d}.",
                k);
            return false;
        }
 
        std::size_t pos_end = 0;
        std::size_t pos_beg = line.find_first_not_of(' ', pos_end);
        pos_end = line.find_first_of(" \n", pos_beg);
 
        if (line.empty() || pos_beg == pos_end ||
            line.compare(pos_beg, 1, "#") == 0)
        {
            k--;
            continue;
        }
 
        if (pos_beg == std::string::npos || pos_end == std::string::npos)
        {
            ERR("TetGenInterface::parseElements(): Error reading id of "
                "tetrahedron {:d}.",
                k);
            return false;
        }
 
        // read node ids
        for (std::size_t i(0); i < n_nodes_per_tet; i++)
        {
            pos_beg = line.find_first_not_of(' ', pos_end);
            pos_end = line.find_first_of(' ', pos_beg);
            if (pos_end == std::string::npos)
            {
                pos_end = line.size();
            }
            if (pos_beg != std::string::npos && pos_end != std::string::npos)
            {
                ids[i] = BaseLib::str2number<std::size_t>(
                             line.substr(pos_beg, pos_end - pos_beg)) -
                         offset;
            }
            else
            {
                ERR("TetGenInterface::parseElements(): Error reading node {:d} "
                    "of tetrahedron {:d}.",
                    i,
                    k);
                return false;
            }
        }
 
        // read region attribute - this is something like material group
        int region(0);
        if (region_attribute)
        {
            pos_beg = line.find_first_not_of(' ', pos_end);
            pos_end = line.find_first_of(' ', pos_beg);
            if (pos_end == std::string::npos)
            {
                pos_end = line.size();
            }
            if (pos_beg != std::string::npos && pos_end != std::string::npos)
            {
                region = BaseLib::str2number<int>(
                    line.substr(pos_beg, pos_end - pos_beg));
            }
            else
            {
                ERR("TetGenInterface::parseElements(): Error reading region "
                    "attribute of tetrahedron {:d}.",
                    k);
                return false;
            }
        }
        // insert new element into vector
        auto** tet_nodes = new MeshLib::Node*[4];
        for (int n = 0; n < 4; n++)
        {
            tet_nodes[n] = nodes[ids[n]];
        }
        elements.push_back(new MeshLib::Tet(tet_nodes));
        materials.push_back(region);
    }
 
    return true;
}
 
bool TetGenInterface::writeTetGenSmesh(
    const std::string& file_name,
    const GeoLib::GEOObjects& geo_objects,
    const std::string& geo_name,
    const std::vector<GeoLib::Point>& attribute_points)
{
    std::vector<GeoLib::Point*> const* const points =
        geo_objects.getPointVec(geo_name);
    std::vector<GeoLib::Surface*> const* const surfaces =
        geo_objects.getSurfaceVec(geo_name);
 
    if (points == nullptr)
    {
        ERR("Geometry {:s} not found.", geo_name);
        return false;
    }
    if (surfaces == nullptr)
    {
        WARN("No surfaces found for geometry {:s}. Writing points only.",
             geo_name);
    }
 
    std::ofstream out(file_name.c_str(), std::ios::out);
    out.precision(std::numeric_limits<double>::digits10);
    // the points header
    const std::size_t nPoints(points->size());
    out << nPoints << " 3\n";
    // the point list
    for (std::size_t i = 0; i < nPoints; ++i)
    {
        out << i << "  " << (*(*points)[i])[0] << " " << (*(*points)[i])[1]
            << " " << (*(*points)[i])[2] << "\n";
    }
    // the surfaces header
    const std::size_t nSurfaces = (surfaces) ? surfaces->size() : 0;
    std::size_t nTotalTriangles(0);
    for (std::size_t i = 0; i < nSurfaces; ++i)
    {
        nTotalTriangles += (*surfaces)[i]->getNumberOfTriangles();
    }
    out << nTotalTriangles << " 1\n";
 
    for (std::size_t i = 0; i < nSurfaces; ++i)
    {
        const std::size_t nTriangles((*surfaces)[i]->getNumberOfTriangles());
        const std::size_t marker(i + 1);  // must NOT be 0!
        // the poly list
        for (std::size_t j = 0; j < nTriangles; ++j)
        {
            const GeoLib::Triangle& tri = *(*(*surfaces)[i])[j];
            out << "3  " << tri[0] << " " << tri[1] << " " << tri[2] << " "
                << marker << "\n";
        }
    }
    out << "0\n";  // the polygon holes list
    // the region attributes list
    if (attribute_points.empty())
    {
        out << "0\n";
    }
    else
    {
        const std::size_t nAttributePoints(attribute_points.size());
        out << nAttributePoints << "\n";
        for (std::size_t i = 0; i < nAttributePoints; ++i)
        {
            out << i + 1 << " " << attribute_points[i][0] << " "
                << attribute_points[i][1] << " " << attribute_points[i][2]
                << " " << 10 * attribute_points[i].getID() << "\n";
        }
    }
    INFO(
        "TetGenInterface::writeTetGenSmesh() - {:d} points and {:d} surfaces "
        "successfully written.",
        nPoints,
        nSurfaces);
    out.close();
    return true;
}
 
bool TetGenInterface::writeTetGenSmesh(
    const std::string& file_name,
    const MeshLib::Mesh& mesh,
    std::vector<MeshLib::Node>& attribute_points) const
{
    if (mesh.getDimension() == 1)
    {
        return false;
    }
 
    const std::vector<MeshLib::Node*>& nodes = mesh.getNodes();
 
    std::ofstream out(file_name.c_str(), std::ios::out);
    out.precision(std::numeric_limits<double>::digits10);
    // the points header
    const std::size_t nPoints(nodes.size());
    out << nPoints << " 3\n";
    // the point list
    for (std::size_t i = 0; i < nPoints; ++i)
    {
        out << i << "  " << (*nodes[i])[0] << " " << (*nodes[i])[1] << " "
            << (*nodes[i])[2] << "\n";
    }
 
    if (mesh.getDimension() == 2)
    {
        write2dElements(out, mesh);
    }
    else
    {
        write3dElements(out, mesh, attribute_points);
    }
 
    out << "0\n";  // the polygon holes list
 
    // the region attributes list
    if (attribute_points.empty())
    {
        out << "0\n";
    }
    else
    {
        const std::size_t nAttributePoints(attribute_points.size());
        out << nAttributePoints << "\n";
        for (std::size_t i = 0; i < nAttributePoints; ++i)
        {
            out << i + 1 << " " << attribute_points[i][0] << " "
                << attribute_points[i][1] << " " << attribute_points[i][2]
                << " " << 10 * attribute_points[i].getID() << "\n";
        }
    }
 
    INFO(
        "TetGenInterface::writeTetGenPoly() - {:d} points and {:d} surfaces "
        "successfully written.",
        nPoints,
        mesh.getNumberOfElements());
    out.close();
    return true;
}
 
void TetGenInterface::write2dElements(std::ofstream& out,
                                      const MeshLib::Mesh& mesh) const
{
    // the surfaces header
    auto const& types = MeshLib::MeshInformation::getNumberOfElementTypes(mesh);
    std::size_t const n_tri =
        (types.find(MeshLib::MeshElemType::TRIANGLE) != types.end())
            ? types.at(MeshLib::MeshElemType::TRIANGLE)
            : 0;
    std::size_t const n_quad =
        (types.find(MeshLib::MeshElemType::QUAD) != types.end())
            ? types.at(MeshLib::MeshElemType::QUAD)
            : 0;
    unsigned const nTotalTriangles = n_tri + 2 * n_quad;
    out << nTotalTriangles << " 1\n";
 
    const std::vector<MeshLib::Element*>& elements = mesh.getElements();
    MeshLib::PropertyVector<int> const* const mat_ids =
        mesh.getProperties().existsPropertyVector<int>("MaterialIDs")
            ? mesh.getProperties().getPropertyVector<int>("MaterialIDs")
            : nullptr;
    const std::size_t nElements(elements.size());
    unsigned element_count(0);
    for (std::size_t i = 0; i < nElements; ++i)
    {
        std::string const matId = mat_ids ? std::to_string((*mat_ids)[i]) : "";
        this->writeElementToFacets(out, *elements[i], element_count, matId);
    }
}
 
void TetGenInterface::write3dElements(
    std::ofstream& out,
    const MeshLib::Mesh& mesh,
    std::vector<MeshLib::Node>& attribute_points) const
{
    const std::vector<MeshLib::Element*>& elements = mesh.getElements();
    const std::size_t nElements(elements.size());
    if (!attribute_points.empty())
    {
        attribute_points.clear();
    }
 
    // get position where number of facets need to be written and figure out
    // worst case of chars that are needed
    const std::streamoff before_elems_pos(out.tellp());
    const unsigned n_spaces(
        static_cast<unsigned>(std::floor(log(nElements * 8))) + 1);
    out << std::string(n_spaces, ' ') << " 1\n";
    auto const* const materialIds =
        mesh.getProperties().getPropertyVector<int>("MaterialIDs");
    unsigned element_count(0);
    for (std::size_t i = 0; i < nElements; ++i)
    {
        if (elements[i]->getDimension() < 3)
        {
            continue;
        }
 
        const unsigned nFaces(elements[i]->getNumberOfNeighbors());
        std::string const mat_id_str =
            materialIds ? std::to_string((*materialIds)[i]) : "";
        for (std::size_t j = 0; j < nFaces; ++j)
        {
            MeshLib::Element const* const neighbor(elements[i]->getNeighbor(j));
 
            if (neighbor && materialIds &&
                (*materialIds)[i] <= (*materialIds)[neighbor->getID()])
            {
                continue;
            }
 
            std::unique_ptr<MeshLib::Element const> const face(
                elements[i]->getFace(j));
            this->writeElementToFacets(out, *face, element_count, mat_id_str);
        }
        if (materialIds)
        {
            attribute_points.emplace_back(
                MeshLib::getCenterOfGravity(*elements[i]).getCoords(),
                (*materialIds)[i]);
        }
    }
    // add number of facets at correct position and jump back
    const std::streamoff after_elems_pos(out.tellp());
    out.seekp(before_elems_pos);
    out << element_count;
    out.seekp(after_elems_pos);
}
 
void TetGenInterface::writeElementToFacets(std::ofstream& out,
                                           const MeshLib::Element& element,
                                           unsigned& element_count,
                                           std::string const& matId)
{
    element_count++;
    if (element.getGeomType() == MeshLib::MeshElemType::TRIANGLE)
    {
        out << "3  " << getNodeIndex(element, 0) << " "
            << getNodeIndex(element, 1) << " " << getNodeIndex(element, 2)
            << " " << matId << " # " << element_count << "\n";
    }
    else if (element.getGeomType() == MeshLib::MeshElemType::QUAD)
    {
        out << "3  " << getNodeIndex(element, 0) << " "
            << getNodeIndex(element, 1) << " " << getNodeIndex(element, 2)
            << " " << matId << " # " << element_count << "\n";
        element_count++;
        out << "3  " << getNodeIndex(element, 0) << " "
            << getNodeIndex(element, 2) << " " << getNodeIndex(element, 3)
            << " " << matId << " # " << element_count << "\n";
    }
}
 
}  // end namespace FileIO