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CreateESGrid

vtk-examples/Cxx/ExplicitStructuredGrid/CreateESGrid


Description

This example demonstrates how (1) to create an explicit structured grid and (2) to convert an explicit structured grid into an unstructured grid or vice versa.

Other languages

See (Python)

Question

If you have a question about this example, please use the VTK Discourse Forum

Code

CreateESGrid.cxx

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkCellArray.h>
#include <vtkDataSetMapper.h>
#include <vtkExplicitStructuredGrid.h>
#include <vtkExplicitStructuredGridToUnstructuredGrid.h>
#include <vtkInteractorStyleRubberBandPick.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPoints.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkUnstructuredGrid.h>
#include <vtkUnstructuredGridToExplicitStructuredGrid.h>

#include <array>
#include <vector>

namespace {

vtkNew<vtkExplicitStructuredGrid>
CreateExplicitStructuredGrid(std::array<int, 3> const& dimensions,
                             std::array<int, 3> const& spacing);

vtkNew<vtkUnstructuredGrid>
ConvertToUnstructuredGrid(vtkExplicitStructuredGrid* grid);

vtkNew<vtkExplicitStructuredGrid>
ConvertToExplicitStructuredGrid(vtkUnstructuredGrid* grid);
} // namespace

int main(int, char*[])
{

  vtkNew<vtkNamedColors> colors;

  std::array<int, 3> dimensions{0, 0, 0};
  std::array<int, 3> spacing{1, 1, 1};
  dimensions = {5, 6, 7};
  spacing = {20, 10, 1};
  auto grid = CreateExplicitStructuredGrid(dimensions, spacing);
  auto ug = ConvertToUnstructuredGrid(grid);
  auto esg = ConvertToExplicitStructuredGrid(ug);

  vtkNew<vtkDataSetMapper> mapper;
  mapper->SetInputData(grid);

  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);
  actor->GetProperty()->EdgeVisibilityOn();
  actor->GetProperty()->LightingOff();
  actor->GetProperty()->SetColor(colors->GetColor3d("Seashell").GetData());

  vtkNew<vtkRenderer> renderer;
  renderer->AddActor(actor);
  renderer->SetBackground(colors->GetColor3d("DarkSlateGray").GetData());

  vtkNew<vtkRenderWindow> window;
  window->AddRenderer(renderer);
  window->SetWindowName("CreateESGrid");
  window->SetSize(1024, 768);
  window->Render();

  auto camera = renderer->GetActiveCamera();
  camera->SetPosition(8.383354, -72.468670, 94.262605);
  camera->SetFocalPoint(42.295234, 21.111537, -0.863606);
  camera->SetViewUp(0.152863, 0.676710, 0.720206);
  camera->SetDistance(137.681759);
  camera->SetClippingRange(78.173985, 211.583658);

  vtkNew<vtkRenderWindowInteractor> interactor;
  interactor->SetRenderWindow(window);
  vtkNew<vtkInteractorStyleRubberBandPick> style;
  interactor->SetInteractorStyle(style);
  window->Render();
  interactor->Start();

  return EXIT_SUCCESS;
}

namespace {
vtkNew<vtkExplicitStructuredGrid>
CreateExplicitStructuredGrid(std::array<int, 3> const& dimensions,
                             std::array<int, 3> const& spacing)
{
  auto ni = dimensions[0];
  auto nj = dimensions[1];
  auto nk = dimensions[2];
  auto si = spacing[0];
  auto sj = spacing[1];
  auto sk = spacing[2];
  vtkNew<vtkPoints> points;
  for (auto z = 0; z < nk * sk; z += sk)
  {
    for (auto y = 0; y < nj * sj; y += sj)
    {
      for (auto x = 0; x < ni * si; x += si)
      {
        points->InsertNextPoint(x, y, z);
      }
    }
  }
  // std::vector < std::vector<int> > cells;
  vtkNew<vtkCellArray> cells;
  for (vtkIdType k = 0; k < nk - 1; ++k)
  {
    for (vtkIdType j = 0; j < nj - 1; ++j)
    {
      for (vtkIdType i = 0; i < ni - 1; ++i)
      {
        // std::cout << "(" << i << ", " << j << ", " << k << ")" << std::endl;
        std::vector<std::array<vtkIdType, 8>> multiIndex;
        multiIndex.push_back({i, i + 1, i + 1, i, i, i + 1, i + 1, i});
        multiIndex.push_back({j, j, j + 1, j + 1, j, j, j + 1, j + 1});
        multiIndex.push_back({k, k, k, k, k + 1, k + 1, k + 1, k + 1});
        // Now let's emulate:
        // pts = np.ravel_multi_index(multi_index, dimensions, order='F')
        cells->InsertNextCell(8);
        std::vector<vtkIdType> cell;
        for (auto idx = 0; idx < 8; ++idx)
        {
          vtkIdType ii = multiIndex[0][idx];
          vtkIdType jj = multiIndex[1][idx];
          vtkIdType kk = multiIndex[2][idx];
          cells->InsertCellPoint(ii + jj * ni + kk * nj * ni);
        }
      }
    }
  }

  vtkNew<vtkExplicitStructuredGrid> grid;
  grid->SetDimensions(ni, nj, nk);
  grid->SetPoints(points);
  grid->SetCells(cells);

  return grid;
}

vtkNew<vtkUnstructuredGrid>
ConvertToUnstructuredGrid(vtkExplicitStructuredGrid* grid)
{
  vtkNew<vtkExplicitStructuredGridToUnstructuredGrid> converter;
  converter->SetInputData(grid);
  converter->Update();
  vtkNew<vtkUnstructuredGrid> ug;
  ug->DeepCopy(converter->GetOutput());
  return ug;
}

vtkNew<vtkExplicitStructuredGrid>
ConvertToExplicitStructuredGrid(vtkUnstructuredGrid* grid)
{
  vtkNew<vtkUnstructuredGridToExplicitStructuredGrid> converter;
  converter->SetInputData(grid);
  // An explicit structured grid.
  // The "BLOCK_I", "BLOCK_J" and"BLOCK_K" cell arrays are required.
  converter->SetInputArrayToProcess(0, 0, 0, 1, "BLOCK_I");
  converter->SetInputArrayToProcess(1, 0, 0, 1, "BLOCK_J");
  converter->SetInputArrayToProcess(2, 0, 0, 1, "BLOCK_K");
  converter->Update();
  vtkNew<vtkExplicitStructuredGrid> esg;
  esg->DeepCopy(converter->GetOutput());
  return esg;
}

} // namespace

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(CreateESGrid)

find_package(VTK COMPONENTS 
  vtkCommonColor
  vtkCommonCore
  vtkCommonDataModel
  vtkFiltersCore
  vtkInteractionStyle
  vtkRenderingContextOpenGL2
  vtkRenderingCore
  vtkRenderingFreeType
  vtkRenderingGL2PSOpenGL2
  vtkRenderingOpenGL2
  QUIET
)

if (NOT VTK_FOUND)
  message("Skipping CreateESGrid: ${VTK_NOT_FOUND_MESSAGE}")
  return ()
endif()
message (STATUS "VTK_VERSION: ${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
  # old system
  include(${VTK_USE_FILE})
  add_executable(CreateESGrid MACOSX_BUNDLE CreateESGrid.cxx )
  target_link_libraries(CreateESGrid PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(CreateESGrid MACOSX_BUNDLE CreateESGrid.cxx )
  target_link_libraries(CreateESGrid PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS CreateESGrid
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build CreateESGrid

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

cd CreateESGrid/build

If VTK is installed:

cmake ..

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

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

make

and run it:

./CreateESGrid

WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.