# InterpolateMeshOnGrid

VTKExamples/Cxx/PolyData/InterpolateMeshOnGrid

### Description

This example resamples a mesh on a grid of points.

### Code

InterpolateMeshOnGrid.cxx

    #include <vtkProperty.h>
    #include <vtkDataSetMapper.h>
    #include <vtkSmartPointer.h>
    #include <vtkCellArray.h>
    #include <vtkPoints.h>
    #include <vtkTriangle.h>
    #include <vtkPolyData.h>
    #include <vtkPointData.h>
    #include <vtkLine.h>
    #include <vtkImageData.h>
    #include <vtkProbeFilter.h>
    #include <vtkDelaunay2D.h>
    #include <vtkXMLPolyDataWriter.h>
    #include <vtkDoubleArray.h>
    #include <vtkMath.h>
    #include <vtkCellLocator.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkFloatArray.h>
    #include <vtkWarpScalar.h>
    #include <vtkVertexGlyphFilter.h>
    #include <vtkInteractorStyleTrackballCamera.h>

    int main(int, char *[])
    {
      // Create a random set of 100 points in the xy-plane in (0,10)x(0,10).
      // If you had instead started with a set of (x,y,z) points, you must copy
      // the zvalues into a FloatArray and set it as the data set's scalars,
      // and then set the z-coordinates to zero
      vtkSmartPointer<vtkPoints> randomPoints =
        vtkSmartPointer<vtkPoints>::New();

      vtkSmartPointer<vtkFloatArray> zvalues =
        vtkSmartPointer<vtkFloatArray>::New();
      zvalues->SetName("ZValues");

      unsigned int gridSize = 10;
      float maxHeight = 5;
      for ( unsigned int i = 0; i < 100; ++i )
      {
        double x = vtkMath::Random(0, gridSize);
        double y = vtkMath::Random(0, gridSize);
        double z = vtkMath::Random(0, maxHeight);

        //randomPoints->InsertNextPoint ( x, y, z);
        randomPoints->InsertNextPoint ( x, y, 0);
        zvalues->InsertNextValue(z);
      }

      // Add the grid points to a polydata object
      vtkSmartPointer<vtkPolyData> randomPolyData =
        vtkSmartPointer<vtkPolyData>::New();
      randomPolyData->SetPoints ( randomPoints );
      randomPolyData->GetPointData()->SetScalars(zvalues);

      // Triangulate the grid points. If you do not have a mesh (points
      // only), the output will not be interpolated!
      vtkSmartPointer<vtkDelaunay2D> randomDelaunay =
        vtkSmartPointer<vtkDelaunay2D>::New();
      randomDelaunay->SetInputData ( randomPolyData );
      randomDelaunay->Update();

      // Create a grid of points to interpolate over
      vtkSmartPointer<vtkPoints> gridPoints =
        vtkSmartPointer<vtkPoints>::New();
      for ( unsigned int x = 0; x < gridSize; x++ )
      {
        for ( unsigned int y = 0; y < gridSize; y++ )
        {
          gridPoints->InsertNextPoint ( x, y, 0);
        }
      }

      // Create a dataset from the grid points
      vtkSmartPointer<vtkPolyData> gridPolyData =
        vtkSmartPointer<vtkPolyData>::New();
      gridPolyData->SetPoints(gridPoints);

      // Perform the interpolation
      vtkSmartPointer<vtkProbeFilter> probeFilter =
        vtkSmartPointer<vtkProbeFilter>::New();
      probeFilter->SetSourceConnection(randomDelaunay->GetOutputPort());
      probeFilter->SetInputData(gridPolyData); //
                                               // Interpolate 'Source' at these points
      probeFilter->Update();

      // Map the output zvalues to the z-coordinates of the data so that
      // we get a surface, rather than a flat grid with interpolated
      // scalars.
      vtkSmartPointer<vtkWarpScalar> gridWarpScalar =
        vtkSmartPointer<vtkWarpScalar>::New();
      gridWarpScalar->SetInputConnection(probeFilter->GetOutputPort());
      gridWarpScalar->Update();

      //////// Setup outputs ////////
      // Output random points
      // Map the output zvalues to the z-coordinates of the data
      vtkSmartPointer<vtkWarpScalar> randomWarpScalar =
        vtkSmartPointer<vtkWarpScalar>::New();
      randomWarpScalar->SetInputConnection(randomDelaunay->GetOutputPort());
      randomWarpScalar->Update();

      vtkSmartPointer<vtkXMLPolyDataWriter> randomWriter =
        vtkSmartPointer<vtkXMLPolyDataWriter>::New();
      randomWriter->SetFileName ( "randomSurface.vtp" );
      randomWriter->SetInputConnection(randomWarpScalar->GetOutputPort());
      randomWriter->Write();

      // Mesh the output grid points
      vtkSmartPointer<vtkDelaunay2D> gridDelaunay =
        vtkSmartPointer<vtkDelaunay2D>::New();
      gridDelaunay->SetInputConnection ( gridWarpScalar->GetOutputPort() );

      vtkSmartPointer<vtkXMLPolyDataWriter> gridWriter =
        vtkSmartPointer<vtkXMLPolyDataWriter>::New();
      gridWriter->SetFileName ( "gridSurface.vtp" );
      gridWriter->SetInputConnection ( gridDelaunay->GetOutputPort() );
      gridWriter->Write();

      ////////// Setup visualization ////////
      vtkSmartPointer<vtkDataSetMapper> randomMapper =
        vtkSmartPointer<vtkDataSetMapper>::New();
      randomMapper->SetInputConnection(randomWarpScalar->GetOutputPort());
      randomMapper->ScalarVisibilityOff();

      vtkSmartPointer<vtkActor> randomActor =
        vtkSmartPointer<vtkActor>::New();
      randomActor->SetMapper(randomMapper);
      randomActor->GetProperty()->SetColor(1.0, 0.0, 0.0); //(R,G,B)
      randomActor->GetProperty()->SetPointSize(3);

      vtkSmartPointer<vtkDataSetMapper> gridMapper =
        vtkSmartPointer<vtkDataSetMapper>::New();
      gridMapper->SetInputConnection(gridDelaunay->GetOutputPort());
      gridMapper->ScalarVisibilityOff();

      vtkSmartPointer<vtkActor> gridActor =
        vtkSmartPointer<vtkActor>::New();
      gridActor->SetMapper(gridMapper);
      gridActor->GetProperty()->SetColor(0.0, 0.0, 1.0); //(R,G,B)
      gridActor->GetProperty()->SetPointSize(3);

      vtkSmartPointer<vtkRenderer> renderer =
        vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
        vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
      renderWindowInteractor->SetInteractorStyle( style );

      renderer->AddActor(randomActor);
      renderer->AddActor(gridActor);

      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(InterpolateMeshOnGrid)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersCore
      vtkFiltersGeneral
      vtkIOXML
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping InterpolateMeshOnGrid: ${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(InterpolateMeshOnGrid MACOSX_BUNDLE InterpolateMeshOnGrid.cxx )
      target_link_libraries(InterpolateMeshOnGrid PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(InterpolateMeshOnGrid MACOSX_BUNDLE InterpolateMeshOnGrid.cxx )
      target_link_libraries(InterpolateMeshOnGrid PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS InterpolateMeshOnGrid
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build InterpolateMeshOnGrid

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

    cd InterpolateMeshOnGrid/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:

    ./InterpolateMeshOnGrid

WINDOWS USERS

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