ImmersedBoundaryMeshWriter.cpp

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*/
 
#include "ImmersedBoundaryMeshWriter.hpp"
 
#include "ImmersedBoundaryArray.hpp"
#include "MathsCustomFunctions.hpp"
#include "UblasCustomFunctions.hpp"
#include "Version.hpp"
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
struct MeshWriterIterators
{
    typename AbstractMesh<ELEMENT_DIM,SPACE_DIM>::NodeIterator* pNodeIter;
    typename ImmersedBoundaryMesh<ELEMENT_DIM,SPACE_DIM>::ImmersedBoundaryElementIterator* pElemIter;
    typename ImmersedBoundaryMesh<ELEMENT_DIM,SPACE_DIM>::ImmersedBoundaryLaminaIterator* pLamIter;
};
 
// Implementation
 
template <unsigned ELEMENT_DIM, unsigned SPACE_DIM>
ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::ImmersedBoundaryMeshWriter(const std::string& rDirectory,
                                                                               const std::string& rBaseName,
                                                                               const bool clearOutputDir)
        : AbstractMeshWriter<ELEMENT_DIM, SPACE_DIM>(rDirectory, rBaseName, clearOutputDir),
          mpMesh(nullptr),
          mpIters(new MeshWriterIterators<ELEMENT_DIM, SPACE_DIM>)
{
    mpIters->pNodeIter = nullptr;
    mpIters->pElemIter = nullptr;
    mpIters->pLamIter = nullptr;
 
    switch (SPACE_DIM)
    {
        case 2:
        {
            geom_point corner_0(0.0, 0.0);
            geom_point corner_1(1.0, 0.0);
            geom_point corner_2(0.0, 1.0);
            geom_point corner_3(1.0, 1.0);
 
            mBoundaryEdges[0] = geom_segment(corner_0, corner_2);  // left edge
            mBoundaryEdges[1] = geom_segment(corner_1, corner_3);  // right edge
            mBoundaryEdges[2] = geom_segment(corner_0, corner_1);  // bottom edge
            mBoundaryEdges[3] = geom_segment(corner_2, corner_3);  // top edge
 
            break;
        }
 
        default:
            NEVER_REACHED;
    }
 
#ifdef CHASTE_VTK
    // Dubious, since we shouldn't yet know what any details of the mesh are.
    mpVtkUnstructedMesh = vtkUnstructuredGrid::New();
#endif //CHASTE_VTK
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::~ImmersedBoundaryMeshWriter()
{
    if (mpIters->pNodeIter)
    {
        delete mpIters->pNodeIter;
        delete mpIters->pElemIter;
        delete mpIters->pLamIter;
    }
 
    delete mpIters;
 
#ifdef CHASTE_VTK
// Dubious, since we shouldn't yet know what any details of the mesh are.
    mpVtkUnstructedMesh->Delete(); // Reference counted
#endif //CHASTE_VTK
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
std::vector<double> ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::GetNextNode()
{
    if (mpMesh)
    {
        // Sanity check
        assert(this->mNumNodes == mpMesh->GetNumNodes());
 
        std::vector<double> coordinates(SPACE_DIM+1);
 
        // Get the node coordinates using the node iterator (thus skipping deleted nodes)
        for (unsigned j=0; j<SPACE_DIM; j++)
        {
            coordinates[j] = (*(mpIters->pNodeIter))->GetPoint()[j];
        }
        coordinates[SPACE_DIM] = (*(mpIters->pNodeIter))->IsBoundaryNode();
 
        ++(*(mpIters->pNodeIter));
 
        return coordinates;
    }
    else
    {
        return AbstractMeshWriter<ELEMENT_DIM,SPACE_DIM>::GetNextNode(); //LCOV_EXCL_LINE fairly sure this is unreachable
    }
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
ImmersedBoundaryElementData ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::GetNextImmersedBoundaryElement()
{
    // Can only be constructed in 2D currently
    //LCOV_EXCL_START
    if constexpr (SPACE_DIM != 2) {
        EXCEPTION("ImmersedBoundaryMeshWriter::GetNextImmersedBoundaryElement is not yet implemetned in 3D!");
    }
    //LCOV_EXCL_STOP
 
    assert(this->mNumElements == mpMesh->GetNumElements());
 
    ImmersedBoundaryElementData elem_data;
    elem_data.NodeIndices.resize((*(mpIters->pElemIter))->GetNumNodes());
    for (unsigned j=0; j<elem_data.NodeIndices.size(); j++)
    {
        elem_data.NodeIndices[j] = (*(mpIters->pElemIter))->GetNodeGlobalIndex(j);
    }
 
    // Set attribute
    elem_data.AttributeValue = (*(mpIters->pElemIter))->GetAttribute();
 
    // Immersed boundary specific data
    auto& element = *(*mpIters->pElemIter);
 
    if (element.GetFluidSource() != nullptr) {
        elem_data.hasFluidSource = true;
        elem_data.fluidSourceIndex = element.GetFluidSource()->GetIndex();
    } else {
        elem_data.hasFluidSource = false;
    }
 
    for (auto cornerNode : element.rGetCornerNodes()) {
        elem_data.cornerNodeIndices.push_back(cornerNode->GetIndex());
    }
 
    elem_data.averageNodeSpacing = element.GetAverageNodeSpacing();
 
    elem_data.isBoundaryElement = element.IsElementOnBoundary();
 
    ++(*(mpIters->pElemIter));
 
    return elem_data;
} // LCOV_EXCL_LINE
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
ImmersedBoundaryElementData ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::GetNextImmersedBoundaryLamina()
{
    //LCOV_EXCL_START
    if constexpr (SPACE_DIM != 2) {
        EXCEPTION("ImmersedBoundaryMeshWriter::GetNextImmersedBoundaryLamina is not yet implemetned in 3D!");
    }
    //LCOV_EXCL_STOP
 
    assert(mNumLaminas == mpMesh->GetNumLaminas());
 
    ImmersedBoundaryElementData lamina_data;
    lamina_data.NodeIndices.resize((*(mpIters->pLamIter))->GetNumNodes());
    for (unsigned j=0; j<lamina_data.NodeIndices.size(); j++)
    {
        lamina_data.NodeIndices[j] = (*(mpIters->pLamIter))->GetNodeGlobalIndex(j);
    }
 
    // Set attribute
    lamina_data.AttributeValue = (*(mpIters->pLamIter))->GetAttribute();
 
    // Immersed boundary specific data
    auto& lamina = *(*mpIters->pLamIter);
 
    try {
        lamina.GetFluidSource();
        // Can't really support 2D laminas at the moment
        //LCOV_EXCL_START
        if (lamina.GetFluidSource() != nullptr) {
            lamina_data.hasFluidSource = true;
            lamina_data.fluidSourceIndex = lamina.GetFluidSource()->GetIndex();
        } else {
            lamina_data.hasFluidSource = false;
        }
        //LCOV_EXCL_STOP
    } catch(Exception& e) {
        lamina_data.hasFluidSource = false;
    }
 
    for (auto cornerNode : lamina.rGetCornerNodes()) {
        lamina_data.cornerNodeIndices.push_back(cornerNode->GetIndex()); // LCOV_EXCL_LINE
    }
 
    lamina_data.averageNodeSpacing = lamina.GetAverageNodeSpacing();
 
    lamina_data.isBoundaryElement = lamina.IsElementOnBoundary();
 
    ++(*(mpIters->pLamIter));
 
    return lamina_data;
} // LCOV_EXCL_LINE
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::WriteVtkUsingMesh(ImmersedBoundaryMesh<ELEMENT_DIM, SPACE_DIM>& rMesh, std::string stamp)
{
#ifdef CHASTE_VTK
    if constexpr (SPACE_DIM == 2)
    {
        // Create VTK mesh
        MakeVtkMesh(rMesh);
        // Now write VTK mesh to file
        //assert(mpVtkUnstructedMesh->CheckAttributes() == 0);
        vtkXMLUnstructuredGridWriter* p_writer = vtkXMLUnstructuredGridWriter::New();
#if VTK_MAJOR_VERSION >= 6
        p_writer->SetInputData(mpVtkUnstructedMesh);
#else
        p_writer->SetInput(mpVtkUnstructedMesh);
#endif
        // Uninitialised stuff arises (see #1079), but you can remove valgrind problems by removing compression:
        // **** REMOVE WITH CAUTION *****
        p_writer->SetCompressor(NULL);
        // **** REMOVE WITH CAUTION *****
 
        std::string vtk_file_name = this->mpOutputFileHandler->GetOutputDirectoryFullPath() + this->mBaseName;
        if (stamp != "")
        {
            vtk_file_name += "_" + stamp;
        }
        vtk_file_name += ".vtu";
 
        p_writer->SetFileName(vtk_file_name.c_str());
        p_writer->Write();
        p_writer->Delete(); // Reference counted
    }
    else
    {
        NEVER_REACHED;
    }
#endif //CHASTE_VTK
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::MakeVtkMesh(ImmersedBoundaryMesh<ELEMENT_DIM, SPACE_DIM>& rMesh)
{
#ifdef CHASTE_VTK
    // Assert mesh is 2D to simplify vtk creation
    if constexpr (SPACE_DIM == 2)
    {
        FindElementOverlaps(rMesh);
 
        // Make the Vtk mesh
        vtkPoints* p_pts = vtkPoints::New(VTK_DOUBLE);
        p_pts->GetData()->SetName("Vertex positions");
 
        // Keep a track of the number of extra points that have been added to the purpose of visualisation
        unsigned num_pts_added = 0;
 
        // Next, we decide how to output the VTK data for elements depending on the type of overlap
        for (auto iter = rMesh.GetElementIteratorBegin(); iter != rMesh.GetElementIteratorEnd(); ++iter)
        {
            unsigned elem_idx = iter->GetIndex();
            unsigned num_nodes = iter->GetNumNodes();
 
            // Case 1: no overlap
            if (mElementParts.size() == 0 || mElementParts[elem_idx].empty())
            {
                vtkCell* p_cell = vtkPolygon::New();
                vtkIdList* p_cell_id_list = p_cell->GetPointIds();
                p_cell_id_list->SetNumberOfIds(num_nodes);
 
                for (unsigned node_local_idx = 0; node_local_idx < num_nodes; ++node_local_idx)
                {
                    // Get node, index and location
                    unsigned global_idx = iter->GetNode(node_local_idx)->GetIndex();
                    const auto& r_location = iter->GetNode(node_local_idx)->rGetLocation();
 
                    p_pts->InsertPoint(global_idx, r_location[0], r_location[1], 0.0);
                    p_cell_id_list->SetId(node_local_idx, global_idx);
                }
 
                mpVtkUnstructedMesh->InsertNextCell(p_cell->GetCellType(), p_cell_id_list);
                p_cell->Delete(); // Reference counted
            }
            else  // Case 2: at least one overlap
            {
                // Get the node index at the start of each part
                const std::vector<unsigned>& start_idx_each_part = mElementParts[iter->GetIndex()];
 
                // Get the number of parts, and put the first index onto the back of the vector for convenience
                const auto num_parts = start_idx_each_part.size();
 
                for (unsigned part = 0; part < num_parts; ++part)
                {
                    const long this_start = start_idx_each_part[part];
                    const long next_start = start_idx_each_part[AdvanceMod(part, 1, num_parts)];
 
                    const long num_nodes_this_part = next_start > this_start ? next_start - this_start : num_nodes + next_start - this_start;
 
                    // Identify the extra points that need to be added
                    std::vector<c_vector<double, SPACE_DIM>> extra_locations;
 
                    // Start of the part
                    {
                        const auto& r_start_pos = iter->GetNode(this_start)->rGetLocation();
                        const auto& r_end_pos = iter->GetNode(AdvanceMod(this_start, -1, num_nodes))->rGetLocation();
 
                        const c_vector<double, SPACE_DIM> vec_a2b = rMesh.GetVectorFromAtoB(r_start_pos, r_end_pos);
                        extra_locations.emplace_back(GetIntersectionOfEdgeWithBoundary(r_start_pos, r_start_pos + vec_a2b));
                    }
 
                    // End of the part
                    {
                        const auto& r_start_pos = iter->GetNode(AdvanceMod(next_start, -1, num_nodes))->rGetLocation();
                        const auto& r_end_pos = iter->GetNode(next_start)->rGetLocation();
 
                        const c_vector<double, SPACE_DIM> vec_a2b = rMesh.GetVectorFromAtoB(r_start_pos, r_end_pos);
                        extra_locations.emplace_back(GetIntersectionOfEdgeWithBoundary(r_start_pos, r_start_pos + vec_a2b));
                    }
 
                    // If the two additional points are not on the same edge of the boundary, we also need to add a corner
                    if (std::fabs(extra_locations.front()[0] - extra_locations.back()[0]) > DBL_EPSILON &&
                        std::fabs(extra_locations.front()[1] - extra_locations.back()[1]) > DBL_EPSILON)
                    {
                        extra_locations.emplace_back(GetNearestCorner(extra_locations.front(), extra_locations.back()));
                    }
 
                    vtkCell* p_cell = vtkPolygon::New();
                    vtkIdList* p_cell_id_list = p_cell->GetPointIds();
                    p_cell_id_list->SetNumberOfIds(num_nodes_this_part + extra_locations.size());
 
                    for (long idx = 0; idx < num_nodes_this_part; ++idx)
                    {
                        unsigned node_idx = AdvanceMod(idx, this_start, num_nodes);
 
                        // Get index and location
                        unsigned global_idx = iter->GetNode(node_idx)->GetIndex();
                        const auto& r_location = iter->GetNode(node_idx)->rGetLocation();
 
                        p_pts->InsertPoint(global_idx, r_location[0], r_location[1], 0.0);
                        p_cell_id_list->SetId(idx, global_idx);
                    }
 
                    // Now add the extra locations
                    if (extra_locations.size() == 2)
                    {
                        const unsigned global_index = rMesh.GetNumNodes() + num_pts_added;
 
                        p_pts->InsertPoint(global_index, extra_locations[1][0], extra_locations[1][1], 0.0);      // end
                        p_pts->InsertPoint(global_index + 1, extra_locations[0][0], extra_locations[0][1], 0.0);  // start
 
                        p_cell_id_list->SetId(num_nodes_this_part, global_index);
                        p_cell_id_list->SetId(num_nodes_this_part + 1, global_index + 1);
 
                        num_pts_added += 2;
                    }
                    else if (extra_locations.size() == 3)
                    {
                        const unsigned global_index = rMesh.GetNumNodes() + num_pts_added;
 
                        p_pts->InsertPoint(global_index, extra_locations[1][0], extra_locations[1][1], 0.0);      // end
                        p_pts->InsertPoint(global_index + 1, extra_locations[2][0], extra_locations[2][1], 0.0);  // corner
                        p_pts->InsertPoint(global_index + 2, extra_locations[0][0], extra_locations[0][1], 0.0);  // start
 
                        p_cell_id_list->SetId(num_nodes_this_part, global_index);
                        p_cell_id_list->SetId(num_nodes_this_part + 1, global_index + 1);
                        p_cell_id_list->SetId(num_nodes_this_part + 2, global_index + 2);
 
                        num_pts_added += 3;
                    }
                    else
                    {
                        NEVER_REACHED;
                    }
 
                    mpVtkUnstructedMesh->InsertNextCell(p_cell->GetCellType(), p_cell_id_list);
                    p_cell->Delete(); // Reference counted
                }
            }
        }
 
        // Finally, output the VTK data for laminas
        for (typename ImmersedBoundaryMesh<ELEMENT_DIM,SPACE_DIM>::ImmersedBoundaryLaminaIterator iter = rMesh.GetLaminaIteratorBegin();
            iter != rMesh.GetLaminaIteratorEnd();
            ++iter)
        {
            unsigned num_nodes = iter->GetNumNodes();
 
            vtkCell* p_cell = vtkPolygon::New();
            vtkIdList* p_cell_id_list = p_cell->GetPointIds();
            p_cell_id_list->SetNumberOfIds(num_nodes);
 
            for (unsigned node_idx = 0; node_idx < num_nodes; node_idx++)
            {
                // Get node, index and location
                Node<SPACE_DIM>* p_node = iter->GetNode(node_idx);
                unsigned global_idx = p_node->GetIndex();
 
                c_vector<double, SPACE_DIM> position = p_node->rGetLocation();
                p_pts->InsertPoint(global_idx, position[0], position[1], 0.0);
 
                p_cell_id_list->SetId(node_idx, global_idx);
            }
 
            mpVtkUnstructedMesh->InsertNextCell(3, p_cell_id_list);
            p_cell->Delete(); // Reference counted
        }
 
        mpVtkUnstructedMesh->SetPoints(p_pts);
        p_pts->Delete(); // Reference counted
    }
    else
    {
        NEVER_REACHED;
    }
#endif //CHASTE_VTK
}
 
//LCOV_EXCL_START
template <>
void ImmersedBoundaryMeshWriter<1, 1>::MakeVtkMesh(ImmersedBoundaryMesh<1, 1>& rMesh)
{
}
//LCOV_EXCL_STOP
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::AddCellData(std::string dataName, std::vector<double> dataPayload)
{
#ifdef CHASTE_VTK
    vtkDoubleArray* p_scalars = vtkDoubleArray::New();
    p_scalars->SetName(dataName.c_str());
    for (unsigned i=0; i<dataPayload.size(); i++)
    {
        p_scalars->InsertNextValue(dataPayload[i]);
    }
 
    vtkCellData* p_cell_data = mpVtkUnstructedMesh->GetCellData();
    p_cell_data->AddArray(p_scalars);
    p_scalars->Delete(); // Reference counted
#endif //CHASTE_VTK
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::AddPointData(std::string dataName, std::vector<double> dataPayload)
{
#ifdef CHASTE_VTK
    vtkDoubleArray* p_scalars = vtkDoubleArray::New();
    p_scalars->SetName(dataName.c_str());
    for (double scalar : dataPayload)
    {
        p_scalars->InsertNextValue(scalar);
    }
 
    vtkPointData* p_point_data = mpVtkUnstructedMesh->GetPointData();
    p_point_data->AddArray(p_scalars);
    p_scalars->Delete(); // Reference counted
#endif //CHASTE_VTK
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::WriteFilesUsingMesh(ImmersedBoundaryMesh<ELEMENT_DIM,SPACE_DIM>& rMesh)
{
    this->mpMeshReader = nullptr;
    mpMesh = &rMesh;
 
    this->mNumNodes = mpMesh->GetNumNodes();
    this->mNumElements = mpMesh->GetNumElements();
    mNumLaminas = mpMesh->GetNumLaminas();
 
    typedef typename AbstractMesh<ELEMENT_DIM,SPACE_DIM>::NodeIterator NodeIterType;
    mpIters->pNodeIter = new NodeIterType(mpMesh->GetNodeIteratorBegin());
 
    typedef typename ImmersedBoundaryMesh<ELEMENT_DIM,SPACE_DIM>::ImmersedBoundaryElementIterator ElemIterType;
    mpIters->pElemIter = new ElemIterType(mpMesh->GetElementIteratorBegin());
 
    typedef typename ImmersedBoundaryMesh<ELEMENT_DIM,SPACE_DIM>::ImmersedBoundaryLaminaIterator LamIterType;
    mpIters->pLamIter = new LamIterType(mpMesh->GetLaminaIteratorBegin());
 
    WriteFiles();
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::WriteFiles()
{
    std::string comment = "# " + ChasteBuildInfo::GetProvenanceString();
 
    // Write node file
    std::string node_file_name = this->mBaseName + ".node";
    out_stream p_node_file = this->mpOutputFileHandler->OpenOutputFile(node_file_name);
 
    // Write the node header
    unsigned num_attr = 0;
    unsigned max_bdy_marker = 1; // as we include boundary node information in the node file
    unsigned num_nodes = this->GetNumNodes();
 
    *p_node_file << num_nodes << "\t";
    *p_node_file << SPACE_DIM << "\t";
    *p_node_file << num_attr << "\t";
    *p_node_file << mpMesh->GetCharacteristicNodeSpacing() << "\t";
    *p_node_file << max_bdy_marker << "\n";
    *p_node_file << std::setprecision(6);
 
    // Write each node's data
    for (unsigned item_num=0; item_num<num_nodes; item_num++)
    {
        std::vector<double> current_item = this->GetNextNode();
        *p_node_file << item_num;
        for (unsigned i=0; i<SPACE_DIM+1; i++)
        {
            *p_node_file << "\t" << current_item[i];
        }
        *p_node_file << "\n";
    }
    *p_node_file << comment << "\n";
    p_node_file->close();
 
    // Write element file
    std::string element_file_name = this->mBaseName + ".elem";
    out_stream p_element_file = this->mpOutputFileHandler->OpenOutputFile(element_file_name);
 
    // Write the element header
    num_attr = 1; //Always write element attributes
    unsigned num_elements = this->GetNumElements();
    *p_element_file << num_elements << "\t" << num_attr << "\n";
 
    // Write each element's data
    for (unsigned item_num=0; item_num<num_elements; item_num++)
    {
        if (SPACE_DIM == 2) // In 2D, write the node indices owned by this element
        {
            // Get data for this element
            ImmersedBoundaryElementData elem_data = this->GetNextImmersedBoundaryElement();
 
            // Get the node indices owned by this element
            std::vector<unsigned> node_indices = elem_data.NodeIndices;
 
            // Write this element's index and the number of nodes owned by it to file
            *p_element_file << item_num <<  "\t" << node_indices.size();
 
            // Write the node indices owned by this element to file
            for (unsigned node_index : node_indices)
            {
                *p_element_file << "\t" << node_index;
            }
 
            *p_element_file << "\t" << elem_data.AttributeValue;
 
            // Has fluid source
            *p_element_file << "\t" << elem_data.hasFluidSource;
 
            // Fluid source index
            if (elem_data.hasFluidSource) {
                *p_element_file << "\t" << elem_data.fluidSourceIndex;
            }
 
            // Corner node indices
            *p_element_file << "\t" << elem_data.cornerNodeIndices.size();
 
            for (auto nodeIndex : elem_data.cornerNodeIndices) {
                *p_element_file << "\t" << nodeIndex;
            }
 
            // Average node spacing
            *p_element_file << "\t" << elem_data.averageNodeSpacing;
 
            // Is boundary element
            *p_element_file << "\t" << elem_data.isBoundaryElement;
 
            // New line
            *p_element_file << "\n";
        }
        else // 3D
        {
        }
    }
    *p_element_file << comment << "\n";
    p_element_file->close();
 
    // Write lamina file
    std::string lamina_file_name = this->mBaseName + ".lam";
    out_stream p_lamina_file = this->mpOutputFileHandler->OpenOutputFile(lamina_file_name);
 
    // Write the lamina header
    num_attr = 1; //Always write element attributes
    unsigned num_laminas = mpMesh->GetNumLaminas();
    *p_lamina_file << num_laminas << "\t" << num_attr << "\n";
 
    // Write each lamina's data
    for (unsigned item_num=0; item_num<num_laminas; item_num++)
    {
        if (SPACE_DIM == 2) // In 2D, write the node indices owned by this element
        {
            // Get data for this element
            ImmersedBoundaryElementData lamina_data = this->GetNextImmersedBoundaryLamina();
 
            // Get the node indices owned by this element
            std::vector<unsigned> node_indices = lamina_data.NodeIndices;
 
            // Write this element's index and the number of nodes owned by it to file
            *p_lamina_file << item_num <<  "\t" << node_indices.size();
 
            // Write the node indices owned by this element to file
            for (unsigned i=0; i<node_indices.size(); i++)
            {
                *p_lamina_file << "\t" << node_indices[i];
            }
 
            *p_lamina_file << "\t" << lamina_data.AttributeValue;
 
            // Has fluid source
            *p_lamina_file << "\t" << lamina_data.hasFluidSource;
 
            // Fluid source index
            if (lamina_data.hasFluidSource) {
                *p_lamina_file << "\t" << lamina_data.fluidSourceIndex; //LCOV_EXCL_LINE
            }
 
            // Corner node indices
            *p_lamina_file << "\t" << lamina_data.cornerNodeIndices.size();
 
            for (auto nodeIndex : lamina_data.cornerNodeIndices) {
                *p_lamina_file << "\t" << nodeIndex; //LCOV_EXCL_LINE
            }
 
            // Average node spacing
            *p_lamina_file << "\t" << lamina_data.averageNodeSpacing;
 
            // Is boundary lamina
            *p_lamina_file << "\t" << lamina_data.isBoundaryElement;
 
 
            // New line
            *p_lamina_file << "\n";
        }
        else // 3D
        {
        }
    }
    *p_lamina_file << comment << "\n";
    p_lamina_file->close();
 
    // Write grid file
    std::string grid_file_name = this->mBaseName + ".grid";
    out_stream p_grid_file = this->mpOutputFileHandler->OpenOutputFile(grid_file_name);
 
    // Write the element header
    unsigned num_gridpts_x = mpMesh->GetNumGridPtsX();
    unsigned num_gridpts_y = mpMesh->GetNumGridPtsY();
 
    *p_grid_file << num_gridpts_x << "\t" << num_gridpts_y << "\n";
 
    // Write grid data
    const multi_array<double, 3>& vel_grids = mpMesh->rGet2dVelocityGrids();
 
    for (unsigned y_idx = 0; y_idx < num_gridpts_y; y_idx ++)
    {
        for (unsigned x_idx = 0; x_idx < num_gridpts_x; x_idx ++)
        {
            *p_grid_file << vel_grids[0][x_idx][y_idx] << "\t";
        }
        *p_grid_file << "\n";
    }
 
    for (unsigned y_idx = 0; y_idx < num_gridpts_y; y_idx ++)
    {
        for (unsigned x_idx = 0; x_idx < num_gridpts_x; x_idx ++)
        {
            *p_grid_file << vel_grids[1][x_idx][y_idx] << "\t";
        }
        *p_grid_file << "\n";
    }
 
    *p_grid_file << comment << "\n";
    p_grid_file->close();
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
void ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::FindElementOverlaps(ImmersedBoundaryMesh<ELEMENT_DIM, SPACE_DIM>& rMesh)
{
    if constexpr (SPACE_DIM == 2)
    {
        // Resize and initialise the vector of overlaps (bools; whether each element has an overlap)
        mElementParts.resize(rMesh.GetNumAllElements());
        for (auto& parts : mElementParts)
        {
            parts.clear();
        }
 
        // We loop over each element and the node index at each discontinuity due to periodic boundaries
        for (auto iter = rMesh.GetElementIteratorBegin(); iter != rMesh.GetElementIteratorEnd(); ++iter)
        {
            for (unsigned node_idx = 0; node_idx < iter->GetNumNodes(); ++node_idx)
            {
                const unsigned prev_idx = AdvanceMod(node_idx, -1, iter->GetNumNodes());
 
                const auto& this_location = iter->GetNode(node_idx)->rGetLocation();
                const auto& prev_location = iter->GetNode(prev_idx)->rGetLocation();
 
                if (norm_inf(this_location - prev_location) > 0.5)
                {
                    mElementParts[iter->GetIndex()].emplace_back(node_idx);
                }
            }
        }
    }
    else
    {
        NEVER_REACHED;
    }
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
c_vector<double, SPACE_DIM> ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::GetIntersectionOfEdgeWithBoundary(
        const c_vector<double, SPACE_DIM>& rStart,
        const c_vector<double, SPACE_DIM>& rEnd)
{
    // Note that this function relies on SPACE_DIM == 2
 
    // Turn the c_vector start and end into a boost::geometry segment object
    geom_point start(rStart[0], rStart[1]);
    geom_point end(rEnd[0], rEnd[1]);
    geom_segment edge(start, end);
 
    // Identify which boundary edge the intersection is with
    std::vector<geom_point> intersections;
    for (const auto& boundary_edge : mBoundaryEdges)
    {
        if (boost::geometry::intersects(edge, boundary_edge))
        {
            boost::geometry::intersection(edge, boundary_edge, intersections);
            break;
        }
    }
 
    // There should be exactly one intersection
    if (intersections.size() != 1)
    {
        NEVER_REACHED;
    }
 
    return Create_c_vector(intersections.front().get<0>(), intersections.front().get<1>());
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
c_vector<double, SPACE_DIM> ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::GetNearestCorner(
        const c_vector<double, SPACE_DIM>& rA, const c_vector<double, SPACE_DIM>& rB) const
{
    // Identify the nearest corner to the average location of the two vectors
    const double x = 0.5 * (rA[0] + rB[0]) < 0.5 ? 0.0 : 1.0;
    const double y = 0.5 * (rA[1] + rB[1]) < 0.5 ? 0.0 : 1.0;
 
    return Create_c_vector(x, y);
}
 
template<unsigned ELEMENT_DIM, unsigned SPACE_DIM>
const std::vector<std::vector<unsigned>>& ImmersedBoundaryMeshWriter<ELEMENT_DIM, SPACE_DIM>::rGetElementParts() const
{
    return mElementParts;
}
 
// Explicit instantiation
template class ImmersedBoundaryMeshWriter<1,1>;
template class ImmersedBoundaryMeshWriter<1,2>;
template class ImmersedBoundaryMeshWriter<1,3>;
template class ImmersedBoundaryMeshWriter<2,2>;
template class ImmersedBoundaryMeshWriter<2,3>;
template class ImmersedBoundaryMeshWriter<3,3>;