ITK/Examples/Meshes/ConvertToVTK

ConvertToVTK.cxx

<source lang="cpp"> // ITK

1. include "itkLineCell.h"
2. include "itkMesh.h"
3. include "itkTriangleCell.h"
4. include "itkQuadrilateralCell.h"

// VTK

1. include <vtkCellArray.h>
2. include <vtkSmartPointer.h>
3. include <vtkUnstructuredGrid.h>
4. include <vtkXMLUnstructuredGridWriter.h>

typedef itk::Mesh< float, 3 > MeshType;

// Functions MeshType::Pointer CreateMeshWithEdges(); void ConvertMeshToUnstructuredGrid(MeshType::Pointer, vtkUnstructuredGrid*);

class VistVTKCellsClass {

 vtkCellArray* m_Cells;
 int* m_LastCell;
 int* m_TypeArray;

public:

 // typedef the itk cells we are interested in
 typedef itk::CellInterface<
                     MeshType::PixelType,
                     MeshType::CellTraits >  CellInterfaceType;

 typedef itk::TriangleCell<CellInterfaceType>      floatTriangleCell;
 typedef itk::QuadrilateralCell<CellInterfaceType> floatQuadrilateralCell;

 // Set the vtkCellArray that will be constructed
 void SetCellArray(vtkCellArray* a)
   {
     m_Cells = a;
   }
 // Set the cell counter pointer
 void SetCellCounter(int* i)
   {
     m_LastCell = i;
   }
 // Set the type array for storing the vtk cell types
 void SetTypeArray(int* i)
   {
     m_TypeArray = i;
   }
 // Visit a triangle and create the VTK_TRIANGLE cell
 void Visit(unsigned long, floatTriangleCell* t)
   {
     m_Cells->InsertNextCell(3,  (vtkIdType*)t->PointIdsBegin());
     m_TypeArray[*m_LastCell] = VTK_TRIANGLE;
     (*m_LastCell)++;
   }
 // Visit a triangle and create the VTK_QUAD cell
 void Visit(unsigned long, floatQuadrilateralCell* t)
   {
     m_Cells->InsertNextCell(4,  (vtkIdType*)t->PointIdsBegin());
     m_TypeArray[*m_LastCell] = VTK_QUAD;
     (*m_LastCell)++;
   }

};

int main(int, char *[]) {

 MeshType::Pointer mesh = CreateMeshWithEdges();
 
 vtkSmartPointer<vtkUnstructuredGrid> unstructuredGrid = vtkSmartPointer<vtkUnstructuredGrid>::New();
 ConvertMeshToUnstructuredGrid(mesh, unstructuredGrid);

 // Write file
 vtkSmartPointer<vtkXMLUnstructuredGridWriter> writer =
   vtkSmartPointer<vtkXMLUnstructuredGridWriter>::New();
 writer->SetFileName("output.vtu");
 writer->SetInputConnection(unstructuredGrid->GetProducerPort());
 writer->Write();

 return EXIT_SUCCESS;

}

MeshType::Pointer CreateMeshWithEdges() {

 MeshType::Pointer  mesh = MeshType::New();

 // Create points
 MeshType::PointType p0,p1,p2,p3;

 p0[0]= -1.0; p0[1]= -1.0; p0[2]= 0.0; // first  point ( -1, -1, 0 )
 p1[0]=  1.0; p1[1]= -1.0; p1[2]= 0.0; // second point (  1, -1, 0 )
 p2[0]=  1.0; p2[1]=  1.0; p2[2]= 0.0; // third  point (  1,  1, 0 )
 p3[0]=  1.0; p3[1]=  1.0; p3[2]= 1.0; // third  point (  1,  1, 1 )

 mesh->SetPoint( 0, p0 );
 mesh->SetPoint( 1, p1 );
 mesh->SetPoint( 2, p2 );
 mesh->SetPoint( 3, p3 );

 std::cout << "Points = " << mesh->GetNumberOfPoints() << std::endl;

 //access points
 typedef MeshType::PointsContainer::Iterator     PointsIterator;

 PointsIterator  pointIterator = mesh->GetPoints()->Begin();

 PointsIterator end = mesh->GetPoints()->End();
 while( pointIterator != end )
   {
   MeshType::PointType p = pointIterator.Value();  // access the point
   std::cout << p << std::endl;                    // print the point
   ++pointIterator;                                // advance to next point
   }

 typedef MeshType::CellType::CellAutoPointer         CellAutoPointer;
 typedef itk::LineCell< MeshType::CellType >         LineType;

 CellAutoPointer line0;
 line0.TakeOwnership(  new LineType  );
 line0->SetPointId(0, 0); // line between points 0 and 1
 line0->SetPointId(1, 1);
 mesh->SetCell( 0, line0);

 CellAutoPointer line1;
 line1.TakeOwnership(  new LineType  );
 line1->SetPointId(0, 1); // line between points 1 and 2
 line1->SetPointId(1, 2);
 mesh->SetCell( 1, line1);

 CellAutoPointer line2;
 line2.TakeOwnership(  new LineType  );
 line2->SetPointId(0, 2); // line between points 2 and 3
 line2->SetPointId(1, 3);
 mesh->SetCell( 2, line2);
 
 /*
 typedef MeshType::CellsContainer::Iterator  CellIterator;
 CellIterator  cellIterator = mesh->GetCells()->Begin();
 CellIterator  CellsEnd          = mesh->GetCells()->End();

 while( cellIterator != CellsEnd )
   {
   MeshType::CellType * cellptr = cellIterator.Value();
   LineType * line = dynamic_cast<LineType *>( cellptr );

   long unsigned int* linePoint0 = line->PointIdsBegin();
   //long unsigned int* linePoint1 = line->PointIdsEnd();
   long unsigned int* linePoint1 = linePoint0+1;
   std::cout << "line first point id: " << *linePoint0 << std::endl;
   std::cout << "line second point id: " << *linePoint1 << std::endl;

   ++cellIterator;
   }
 */
 return mesh;

}

void ConvertMeshToUnstructuredGrid(MeshType::Pointer mesh, vtkUnstructuredGrid* unstructuredGrid) {

 // Get the number of points in the mesh
 int numPoints = mesh->GetNumberOfPoints();
 if(numPoints == 0)
   {
   mesh->Print(std::cerr);
   std::cerr << "no points in Grid " << std::endl;
   exit(-1);
   }

 // Create the vtkPoints object and set the number of points
 vtkPoints* vpoints = vtkPoints::New();
 vpoints->SetNumberOfPoints(numPoints);
 // iterate over all the points in the itk mesh filling in
 // the vtkPoints object as we go
 MeshType::PointsContainer::Pointer points = mesh->GetPoints();
 for(MeshType::PointsContainer::Iterator i = points->Begin();
     i != points->End(); ++i)
   {
   // Get the point index from the point container iterator
   int idx = i->Index();
   // Set the vtk point at the index with the the coord array from itk
   // itk returns a const pointer, but vtk is not const correct, so
   // we have to use a const cast to get rid of the const
   vpoints->SetPoint(idx, const_cast<float*>(i->Value().GetDataPointer()));
   }
 // Set the points on the vtk grid
 unstructuredGrid->SetPoints(vpoints);

 // Now create the cells using the MulitVisitor
 // 1. Create a MultiVisitor
 MeshType::CellType::MultiVisitor::Pointer mv =
   MeshType::CellType::MultiVisitor::New();
 // 2. Create a triangle and quadrilateral visitor
 typedef itk::CellInterfaceVisitorImplementation<
   float, MeshType::CellTraits,
   itk::TriangleCell< itk::CellInterface<MeshType::PixelType, MeshType::CellTraits > >,
   VistVTKCellsClass> TriangleVisitor;

 typedef itk::CellInterfaceVisitorImplementation<
   float, MeshType::CellTraits,
   itk::QuadrilateralCell< itk::CellInterface<MeshType::PixelType, MeshType::CellTraits > >,
   VistVTKCellsClass> QuadrilateralVisitor;

 TriangleVisitor::Pointer tv = TriangleVisitor::New();
 QuadrilateralVisitor::Pointer qv =  QuadrilateralVisitor::New();
 // 3. Set up the visitors
 int vtkCellCount = 0; // running counter for current cell being inserted into vtk
 int numCells = mesh->GetNumberOfCells();
 int *types = new int[numCells]; // type array for vtk
 // create vtk cells and estimate the size
 vtkCellArray* cells = vtkCellArray::New();
 cells->EstimateSize(numCells, 4);
 // Set the TypeArray CellCount and CellArray for both visitors
 tv->SetTypeArray(types);
 tv->SetCellCounter(&vtkCellCount);
 tv->SetCellArray(cells);
 qv->SetTypeArray(types);
 qv->SetCellCounter(&vtkCellCount);
 qv->SetCellArray(cells);
 // add the visitors to the multivisitor
 mv->AddVisitor(tv);
 mv->AddVisitor(qv);
 // Now ask the mesh to accept the multivisitor which
 // will Call Visit for each cell in the mesh that matches the
 // cell types of the visitors added to the MultiVisitor
 mesh->Accept(mv);

 // Now set the cells on the vtk grid with the type array and cell array
 unstructuredGrid->SetCells(types, cells);
 std::cout << "Unstructured grid has " << unstructuredGrid->GetNumberOfCells() << " cells." << std::endl;

 // Clean up vtk objects (no vtkSmartPointer ... )
 cells->Delete();
 vpoints->Delete();

} </source>

CMakeLists.txt

<syntaxhighlight lang="cmake"> cmake_minimum_required(VERSION 3.9.5)

project(ConvertToVTK)

find_package(ITK REQUIRED) include(${ITK_USE_FILE}) if (ITKVtkGlue_LOADED)

 find_package(VTK REQUIRED)
 include(${VTK_USE_FILE})

endif()

add_executable(ConvertToVTK MACOSX_BUNDLE ConvertToVTK.cxx)

if( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ConvertToVTK ITKReview ${ITK_LIBRARIES})

else( "${ITK_VERSION_MAJOR}" LESS 4 )

 target_link_libraries(ConvertToVTK ${ITK_LIBRARIES})

endif( "${ITK_VERSION_MAJOR}" LESS 4 )

</syntaxhighlight>

Download and Build ConvertToVTK

Click here to download ConvertToVTK and its CMakeLists.txt file. Once the tarball ConvertToVTK.tar has been downloaded and extracted,

cd ConvertToVTK/build

• If ITK is installed:

cmake ..

• If ITK is not installed but compiled on your system, you will need to specify the path to your ITK build:

cmake -DITK_DIR:PATH=/home/me/itk_build ..

Build the project:

make

and run it:

./ConvertToVTK

WINDOWS USERS PLEASE NOTE: Be sure to add the ITK bin directory to your path. This will resolve the ITK dll's at run time.

Building All of the Examples

Many of the examples in the ITK Wiki Examples Collection require VTK. You can build all of the the examples by following these instructions. If you are a new VTK user, you may want to try the Superbuild which will build a proper ITK and VTK.

ItkVtkGlue

ITK >= 4

For examples that use QuickView (which depends on VTK), you must have built ITK with Module_ITKVtkGlue=ON.

ITK < 4

Some of the ITK Examples require VTK to display the images. If you download the entire ITK Wiki Examples Collection, the ItkVtkGlue directory will be included and configured. If you wish to just build a few examples, then you will need to download ItkVtkGlue and build it. When you run cmake it will ask you to specify the location of the ItkVtkGlue binary directory.