ElevationFilter

#include <vtkActor.h>
#include <vtkCamera.h>
#include <vtkDelaunay2D.h>
#include <vtkElevationFilter.h>
#include <vtkFloatArray.h>
#include <vtkLookupTable.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkXMLPolyDataWriter.h>

// For compatibility with new VTK generic data arrays
#ifdef vtkGenericDataArray_h
#define InsertNextTupleValue InsertNextTypedTuple
#endif

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

  // Create a grid of points (height/terrain map)
  vtkNew<vtkPoints> points;

  unsigned int gridSize = 10;
  for (unsigned int x = 0; x < gridSize; x++)
  {
    for (unsigned int y = 0; y < gridSize; y++)
    {
      points->InsertNextPoint(x, y, (x + y) / (y + 1));
    }
  }

  double bounds[6];
  points->GetBounds(bounds);

  // Add the grid points to a polydata object
  vtkNew<vtkPolyData> inputPolyData;
  inputPolyData->SetPoints(points);

  // Triangulate the grid points
  vtkNew<vtkDelaunay2D> delaunay;
  delaunay->SetInputData(inputPolyData);
  delaunay->Update();

  vtkNew<vtkElevationFilter> elevationFilter;
  elevationFilter->SetInputConnection(delaunay->GetOutputPort());
  elevationFilter->SetLowPoint(0.0, 0.0, bounds[4]);
  elevationFilter->SetHighPoint(0.0, 0.0, bounds[5]);
  elevationFilter->Update();

  vtkNew<vtkPolyData> output;
  output->ShallowCopy(dynamic_cast<vtkPolyData*>(elevationFilter->GetOutput()));

  vtkFloatArray* elevation = dynamic_cast<vtkFloatArray*>(
      output->GetPointData()->GetArray("Elevation"));

  // Create the color map
  vtkNew<vtkLookupTable> colorLookupTable;
  colorLookupTable->SetTableRange(bounds[4], bounds[5]);
  colorLookupTable->Build();

  // Generate the colors for each point based on the color map
  vtkNew<vtkUnsignedCharArray> colors;
  colors->SetNumberOfComponents(3);
  colors->SetName("Colors");

  for (vtkIdType i = 0; i < output->GetNumberOfPoints(); i++)
  {
    double val = elevation->GetValue(i);
    // std::cout << "val: " << val << std::endl;

    double dcolor[3];
    colorLookupTable->GetColor(val, dcolor);
    // std::cout << "dcolor: " << dcolor[0] << " " << dcolor[1] << " " <<
    // dcolor[2] << std::endl;
    unsigned char color[3];
    for (unsigned int j = 0; j < 3; j++)
    {
      color[j] = 255 * dcolor[j] / 1.0;
    }
    // std::cout << "color: " << (int)color[0] << " " << (int)color[1] << " " <<
    // (int)color[2] << std::endl;

    colors->InsertNextTupleValue(color);
  }

  output->GetPointData()->AddArray(colors);

  // Visualize
  vtkNew<vtkPolyDataMapper> mapper;
  mapper->SetInputData(output);

  vtkNew<vtkActor> actor;
  actor->SetMapper(mapper);

  vtkNew<vtkRenderer> renderer;
  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(renderer);
  renderWindow->SetWindowName("ElevationFilter");

  vtkNew<vtkRenderWindowInteractor> renderWindowInteractor;
  renderWindowInteractor->SetRenderWindow(renderWindow);

  renderer->AddActor(actor);
  renderer->SetBackground(namedColors->GetColor3d("ForestGreen").GetData());

  // z-axis points upwards and y-axis is lower right edge.
  auto camera = renderer->GetActiveCamera();
  camera->SetPosition(-13.3586, 20.7305, 22.5147);
  camera->SetFocalPoint(4.5, 4.5, 4.5);
  camera->SetViewUp(0.506199, -0.328212, 0.797521);
  camera->SetDistance(30.1146);
  camera->SetClippingRange(14.3196, 50.0698);

  renderWindow->Render();

  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ElevationFilter)

find_package(VTK COMPONENTS 
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "ElevationFilter: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
add_executable(ElevationFilter MACOSX_BUNDLE ElevationFilter.cxx )
  target_link_libraries(ElevationFilter PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS ElevationFilter
  MODULES ${VTK_LIBRARIES}
)

cd ElevationFilter/build

cmake ..

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

make

./ElevationFilter