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ExtractOutsideSurface

vtk-examples/Cxx/PolyData/ExtractOutsideSurface


Description

This example extracts the outer surface of a multiple surface vtkPolyData model. The example assumes the outside surface is closed and there is only one outside surface. It also assumes that the center of the model lies inside the outer surface.

The example casts a ray from outside the bounds of the model into the center of the model. It uses a vtkCellLocator to intersect the ray with the model. The intersected cell is used as a seed to the [vtkPolyData](https://www.vtk.org/doc/nightly/html/classvtkPolyData.html#details)ConnectivityFilter which is run with the extraction mode set to CellSeededRegions.

If run without arguments, the example generates a small (in area) sphere inside a large (in area) sphere. The inner sphere has more cells than the outer sphere, but should not be extracted.

The gold model is the original vtkPolyData and the blue model is the outer surface.

You can try your own surface by specifying a XML PolyData file (.vtp) on the command line.

Seealso

RemoveOutsideSurface removes the outside surface.

Question

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

Code

ExtractOutsideSurface.cxx

#include <vtkActor.h>
#include <vtkAppendPolyData.h>
#include <vtkCellLocator.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPolyDataConnectivityFilter.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>
#include <vtkTriangleFilter.h>
#include <vtkXMLPolyDataReader.h>

int main(int argc, char* argv[])
{
  // PolyData to process
  vtkSmartPointer<vtkPolyData> polyData;

  if (argc > 1)
  {
    vtkNew<vtkXMLPolyDataReader> reader;
    reader->SetFileName(argv[1]);
    reader->Update();
    polyData = reader->GetOutput();
  }
  else
  {
    // Small sphere with most polgons
    vtkNew<vtkSphereSource> sphereSource1;
    sphereSource1->SetThetaResolution(10);
    sphereSource1->SetPhiResolution(10);
    sphereSource1->SetCenter(5, 5, 5);
    sphereSource1->SetRadius(1.5);

    // Large sphere with least polygons
    vtkNew<vtkSphereSource> sphereSource2;
    sphereSource2->SetRadius(10);
    sphereSource2->SetCenter(10, 1, 10);

    vtkNew<vtkAppendPolyData> appendFilter;
    appendFilter->AddInputConnection(sphereSource1->GetOutputPort());
    appendFilter->AddInputConnection(sphereSource2->GetOutputPort());
    appendFilter->Update();
    polyData = appendFilter->GetOutput();
  }

  double center[3], bounds[6];
  polyData->GetCenter(center);
  std::cout << "Center of data is: " << center[0] << ", " << center[1] << ", "
            << center[2] << std::endl;
  polyData->GetPoints()->GetBounds(bounds);
  std::cout << "Bounds of data is: " << bounds[0] << ", " << bounds[1] << ", "
            << bounds[2] << ", " << bounds[3] << ", " << bounds[4] << ", "
            << bounds[5] << std::endl;

  // Build a cell locator.
  vtkNew<vtkCellLocator> cellLocator;
  cellLocator->SetDataSet(polyData);
  cellLocator->BuildLocator();

  // Now fire a ray from outside the bounds to the center and find a
  // cell. This cell should be on the outside surface
  double rayStart[3];
  for (unsigned int i = 0; i < 3; i++)
  {
    rayStart[i] = bounds[2 * i + 1] * 1.1;
  }

  vtkIdType cellId = -1;
  double xyz[3], t, pcoords[3];
  int subId;

  cellLocator->IntersectWithLine(rayStart, center, 0.0001, t, xyz, pcoords,
                                 subId, cellId);
  std::cout << "Id of cell on outside surface: " << cellId << std::endl;

  vtkNew<vtkPolyDataConnectivityFilter> connectivityFilter;
  connectivityFilter->SetInputData(polyData);
  connectivityFilter->SetExtractionModeToCellSeededRegions();
  connectivityFilter->InitializeSeedList();
  connectivityFilter->AddSeed(cellId);

  // Create a mapper and actor for original data
  vtkNew<vtkPolyDataMapper> originalMapper;
  originalMapper->SetInputData(polyData);

  vtkNew<vtkNamedColors> colors;

  vtkNew<vtkActor> originalActor;
  originalActor->SetMapper(originalMapper);
  originalActor->GetProperty()->BackfaceCullingOn();
  originalActor->GetProperty()->SetOpacity(0.6);
  originalActor->GetProperty()->SetColor(colors->GetColor3d("Gold").GetData());

  // Create a mapper and actor for extracted data
  vtkNew<vtkPolyDataMapper> extractedMapper;
  extractedMapper->SetInputConnection(connectivityFilter->GetOutputPort());

  vtkNew<vtkActor> extractedActor;
  extractedActor->GetProperty()->SetColor(
      colors->GetColor3d("Peacock").GetData());
  extractedActor->SetMapper(extractedMapper);
  extractedActor->GetProperty()->SetOpacity(0.6);
  extractedActor->GetProperty()->BackfaceCullingOn();

  // Create a renderer
  vtkNew<vtkRenderer> renderer;
  renderer->AddActor(originalActor);
  renderer->AddActor(extractedActor);

  renderer->GradientBackgroundOn();
  renderer->SetBackground2(colors->GetColor3d("Beige").GetData());
  renderer->SetBackground(colors->GetColor3d("DarkSlateGray").GetData());

  extractedActor->SetPosition((bounds[1] - bounds[0]) / 1.9, 0, 0);
  originalActor->SetPosition(-(bounds[1] - bounds[0]) / 1.9, 0, 0);
  // Create a render window
  vtkNew<vtkRenderWindow> renwin;
  renwin->AddRenderer(renderer);
  renwin->SetSize(512, 512);
  renwin->SetWindowName("ExtractOutsideSurface");

  // Create an interactor
  vtkNew<vtkRenderWindowInteractor> iren;
  iren->SetRenderWindow(renwin);
  renwin->Render();
  iren->Initialize();
  iren->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(ExtractOutsideSurface)

find_package(VTK COMPONENTS 
  CommonColor
  CommonCore
  CommonDataModel
  FiltersCore
  FiltersSources
  IOXML
  InteractionStyle
  RenderingContextOpenGL2
  RenderingCore
  RenderingFreeType
  RenderingGL2PSOpenGL2
  RenderingOpenGL2
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "ExtractOutsideSurface: 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(ExtractOutsideSurface MACOSX_BUNDLE ExtractOutsideSurface.cxx )
  target_link_libraries(ExtractOutsideSurface PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS ExtractOutsideSurface
  MODULES ${VTK_LIBRARIES}
)

Download and Build ExtractOutsideSurface

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

cd ExtractOutsideSurface/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:

./ExtractOutsideSurface

WINDOWS USERS

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