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StructuredGrid

vtk-examples/Cxx/StructuredGrid/StructuredGrid


Description

This example reads and writes points into a structured grid.

The structured grid is colored by point data. However there is an option to color by cell data.

Demonstration code is also provided to list cells and their Ids along with listing point Ids shared between cells.

Question

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

Code

StructuredGrid.cxx

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkCellData.h>
#include <vtkCellIterator.h>
#include <vtkDataSetMapper.h>
#include <vtkDoubleArray.h>
#include <vtkLookupTable.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkStructuredGrid.h>

#include <iterator>
#include <map>
#include <set>

#define USE_POINT_DATA
// Uncomment the next line if you want to use cell data instead
//#undef USE_POINT_DATA

int main(int, char*[])
{
  vtkNew<vtkNamedColors> colors;

  size_t nx = 2, ny = 3, nz = 2;
  auto dataSize = nx * ny * nz;

  vtkNew<vtkDoubleArray> pointValues;
  pointValues->SetNumberOfComponents(1);
  pointValues->SetNumberOfTuples(dataSize);
  for (size_t i = 0; i < dataSize; ++i)
  {
    pointValues->SetValue(i, i);
  }

  auto numberOfCells = (nx - 1) * (ny - 1) * (nz - 1);
  vtkNew<vtkDoubleArray> cellValues;
  cellValues->SetNumberOfTuples(numberOfCells);
  for (size_t i = 0; i < numberOfCells; ++i)
  {
    cellValues->SetValue(i, i);
  }

  vtkNew<vtkPoints> points;
  auto x = 0.0;
  auto y = 0.0;
  auto z = 0.0;
  for (unsigned int k = 0; k < nz; k++)
  {
    z += 2.0;
    for (unsigned int j = 0; j < ny; j++)
    {
      y += 1.0;
      for (unsigned int i = 0; i < nx; i++)
      {
        x += .5;
        points->InsertNextPoint(x, y, z);
      }
    }
  }

  // Create a grid
  vtkNew<vtkStructuredGrid> structuredGrid;
  // Specify the dimensions of the grid
  structuredGrid->SetDimensions(static_cast<int>(nx), static_cast<int>(ny),
                                static_cast<int>(nz));
  structuredGrid->SetPoints(points);
  structuredGrid->GetCellData()->SetScalars(cellValues);
  structuredGrid->GetPointData()->SetScalars(pointValues);

  // The key is the cell Id and the value is a set of corresponding point Ids.
  std::map<vtkIdType, std::set<vtkIdType>> cellPointIds;
  vtkCellIterator* it = structuredGrid->NewCellIterator();
  for (it->InitTraversal(); !it->IsDoneWithTraversal(); it->GoToNextCell())
  {
    vtkIdList* pointIds = it->GetPointIds();
    std::set<vtkIdType> ptIds;
    for (vtkIdType* id = pointIds->begin(); id != pointIds->end(); ++id)
    {
      ptIds.insert(*id);
    }
    cellPointIds[it->GetCellId()] = ptIds;
  }
  it->Delete();

  std::cout << "Cells and their points" << std::endl;
  for (auto cell : cellPointIds)
  {
    std::cout << "Cell Id: " << cell.first << " Point Ids: ";
    for (auto id = cell.second.begin(); id != cell.second.end(); ++id)
      if (id != std::prev(cell.second.end()))
      {
        std::cout << *id << ", ";
      }
      else
      {
        std::cout << *id << std::endl;
      }
  }

  // The key is the point Id and the value is a set of corresponding cell Ids.
  std::map<vtkIdType, std::set<vtkIdType>>
      commonPointIds; // = cellPointIds.begin()->second;
  for (auto cell : cellPointIds)
  {
    for (auto pointId : cell.second)
    {
      commonPointIds[pointId].insert(cell.first);
    }
  }

  std::cout << "Point Ids shared between cells" << std::endl;
  for (auto point = commonPointIds.begin(); point != commonPointIds.end();
       ++point)
  {
    if (point->second.size() > 1)
    {
      std::cout << "Point Id: " << point->first << " CellIds: ";
      for (auto cellId = point->second.begin(); cellId != point->second.end();
           ++cellId)
      {
        if (cellId != std::prev(point->second.end()))
        {
          std::cout << *cellId << ", ";
        }
        else
        {
          std::cout << *cellId << std::endl;
        }
      }
    }
  }

#if defined(USE_POINT_DATA)
  // Use the point data
  // Map the scalar values in the image to colors with a lookup table:
  vtkNew<vtkLookupTable> lut;
  lut->SetNumberOfTableValues(dataSize);
  lut->Build();

  // Create a mapper and actor
  vtkNew<vtkDataSetMapper> mapper;
  mapper->SetInputData(structuredGrid);
  mapper->SetLookupTable(lut);
  mapper->SetScalarRange(0, dataSize - 1);
  mapper->ScalarVisibilityOn();
#else
  // Use the cell data
  vtkNew<vtkLookupTable> lut;
  lut->SetNumberOfTableValues(numberOfCells);
  lut->Build();
  // Assign some specific colors in this case
  lut->SetTableValue(0, colors->GetColor4d("Red").GetData());
  lut->SetTableValue(numberOfCells - 1, colors->GetColor4d("Banana").GetData());

  // Create a mapper and actor
  vtkNew<vtkDataSetMapper> mapper;
  mapper->SetInputData(structuredGrid);
  mapper->SetLookupTable(lut);
  mapper->SetScalarRange(0, numberOfCells - 1);
  // mapper->ScalarVisibilityOff();
#endif
  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);

  // Create a renderer, render window, and interactor
  vtkNew<vtkRenderer> ren;
  vtkNew<vtkRenderWindow> renWin;
  renWin->AddRenderer(ren);
  vtkNew<vtkRenderWindowInteractor> iRen;
  iRen->SetRenderWindow(renWin);

  // Add the actor to the scene
  ren->AddActor(actor);
  ren->SetBackground(colors->GetColor3d("SlateGray").GetData());

  ren->GetActiveCamera()->Azimuth(60);
  ren->GetActiveCamera()->Elevation(-45);
  ren->GetActiveCamera()->Dolly(1.2);
  ren->ResetCamera();

  // Render and interact
  renWin->Render();
  renWin->SetSize(800, 800);
  renWin->SetWindowName("StructuredGrid");
  iRen->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(StructuredGrid)

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

if (NOT VTK_FOUND)
  message("Skipping StructuredGrid: ${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(StructuredGrid MACOSX_BUNDLE StructuredGrid.cxx )
  target_link_libraries(StructuredGrid PRIVATE ${VTK_LIBRARIES})
else ()
  # include all components
  add_executable(StructuredGrid MACOSX_BUNDLE StructuredGrid.cxx )
  target_link_libraries(StructuredGrid PRIVATE ${VTK_LIBRARIES})
  # vtk_module_autoinit is needed
  vtk_module_autoinit(
    TARGETS StructuredGrid
    MODULES ${VTK_LIBRARIES}
    )
endif ()

Download and Build StructuredGrid

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

cd StructuredGrid/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:

./StructuredGrid

WINDOWS USERS

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