DotProduct

Description¶

This example demonstrates how to take the pixel-wise dot product of two vector images. The output is a scalar image.

Two images, each 2x2x1, are created and filled with 3-vectors. The dot product of each pair of corresponding pixels is produced by the vtkImageDotProduct filter and output to the screen.

Question

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Code¶

DotProduct.cxx

#include <vtkActor.h>
#include <vtkArrowSource.h>
#include <vtkGlyph3DMapper.h>
#include <vtkImageActor.h>
#include <vtkImageCast.h>
#include <vtkImageData.h>
#include <vtkImageDotProduct.h>
#include <vtkImageMapper3D.h>
#include <vtkImageMathematics.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>

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

  // Create an image
  vtkNew<vtkImageData> image1;
  image1->SetExtent(0, 1, 0, 1, 0, 0);
  image1->AllocateScalars(VTK_FLOAT, 3);

  int coord[3];
  float* pixel;

  // Fill the image with vectors
  coord[0] = 0;
  coord[1] = 0;
  coord[2] = 0;
  pixel = static_cast<float*>(image1->GetScalarPointer(coord));
  pixel[0] = 1.0;
  pixel[1] = 0.0;
  pixel[2] = 0.0;

  coord[0] = 0;
  coord[1] = 1;
  coord[2] = 0;
  pixel = static_cast<float*>(image1->GetScalarPointer(coord));
  pixel[0] = 0.0;
  pixel[1] = 1.0;
  pixel[2] = 0.0;

  coord[0] = 1;
  coord[1] = 0;
  coord[2] = 0;
  pixel = static_cast<float*>(image1->GetScalarPointer(coord));
  pixel[0] = 1.0;
  pixel[1] = 0.0;
  pixel[2] = 0.0;

  coord[0] = 1;
  coord[1] = 1;
  coord[2] = 0;
  pixel = static_cast<float*>(image1->GetScalarPointer(coord));
  pixel[0] = 0.0;
  pixel[1] = 1.0;
  pixel[2] = 0.0;

  // Create another image.
  vtkNew<vtkImageData> image2;
  image2->SetExtent(0, 1, 0, 1, 0, 0);
  image2->AllocateScalars(VTK_FLOAT, 3);

  // Fill the image with vectors.
  coord[0] = 0;
  coord[1] = 0;
  coord[2] = 0;
  pixel = static_cast<float*>(image2->GetScalarPointer(coord));
  pixel[0] = 1.0;
  pixel[1] = 0.0;
  pixel[2] = 0.0;

  coord[0] = 0;
  coord[1] = 1;
  coord[2] = 0;
  pixel = static_cast<float*>(image2->GetScalarPointer(coord));
  pixel[0] = 1.0;
  pixel[1] = 0.0;
  pixel[2] = 0.0;

  coord[0] = 1;
  coord[1] = 0;
  coord[2] = 0;
  pixel = static_cast<float*>(image2->GetScalarPointer(coord));
  pixel[0] = 0.5;
  pixel[1] = 0.0;
  pixel[2] = 0.0;

  coord[0] = 1;
  coord[1] = 1;
  coord[2] = 0;
  pixel = static_cast<float*>(image2->GetScalarPointer(coord));
  pixel[0] = 0.5;
  pixel[1] = 0.0;
  pixel[2] = 0.0;

  // Compute the dot product of the images pixel wise.
  vtkNew<vtkImageDotProduct> dotProductFilter;
  dotProductFilter->SetInput1Data(image1);
  dotProductFilter->SetInput2Data(image2);
  dotProductFilter->Update();
  std::cout << "Output is of type: "
            << dotProductFilter->GetOutput()->GetScalarTypeAsString()
            << std::endl;

  vtkNew<vtkImageMathematics> imageMath;
  imageMath->SetOperationToMultiplyByK();
  imageMath->SetConstantK(255.0);
  imageMath->SetInputConnection(dotProductFilter->GetOutputPort());
  imageMath->Update();

  vtkNew<vtkImageCast> imageCast;
  imageCast->SetOutputScalarTypeToUnsignedChar();
  imageCast->SetInputConnection(imageMath->GetOutputPort());
  imageCast->Update();

  vtkNew<vtkImageActor> dotProductActor;
  dotProductActor->GetMapper()->SetInputConnection(imageCast->GetOutputPort());

  // Display output to the terminal.
  for (vtkIdType i = 0; i < 2; i++)
  {
    for (vtkIdType j = 0; j < 2; j++)
    {
      coord[0] = i;
      coord[1] = j;
      coord[2] = 0;
      pixel = static_cast<float*>(
          dotProductFilter->GetOutput()->GetScalarPointer(coord));
      std::cout << "Pixel (" << i << ", " << j << ") : " << pixel[0]
                << std::endl;
    }
  }

  image1->GetPointData()->SetActiveVectors("ImageScalars");
  image2->GetPointData()->SetActiveVectors("ImageScalars");

  vtkNew<vtkArrowSource> arrowSource;

  vtkNew<vtkGlyph3DMapper> glyph3Dmapper1;
  glyph3Dmapper1->SetSourceConnection(arrowSource->GetOutputPort());
  glyph3Dmapper1->SetInputData(image1);
  glyph3Dmapper1->Update();

  vtkNew<vtkActor> actor1;
  actor1->SetMapper(glyph3Dmapper1);

  vtkNew<vtkGlyph3DMapper> glyph3Dmapper2;
  glyph3Dmapper2->SetSourceConnection(arrowSource->GetOutputPort());
  glyph3Dmapper2->SetInputData(image2);
  glyph3Dmapper2->Update();

  vtkNew<vtkActor> actor2;
  actor2->SetMapper(glyph3Dmapper2);

  // Define viewport ranges.
  // (xmin, ymin, xmax, ymax)
  double leftViewport[4] = {0.0, 0.0, 0.33, 1.0};
  double centerViewport[4] = {0.33, 0.0, 0.66, 1.0};
  double rightViewport[4] = {0.66, 0.0, 1.0, 1.0};

  // Create a renderer, render window, and interactor.
  vtkNew<vtkRenderer> leftRenderer;
  leftRenderer->SetViewport(leftViewport);
  leftRenderer->SetBackground(colors->GetColor3d("DimGray").GetData());

  vtkNew<vtkRenderer> centerRenderer;
  centerRenderer->SetViewport(centerViewport);
  centerRenderer->SetBackground(colors->GetColor3d("DimGray").GetData());

  vtkNew<vtkRenderer> rightRenderer;
  rightRenderer->SetViewport(rightViewport);
  rightRenderer->SetBackground(colors->GetColor3d("DimGray").GetData());

  vtkNew<vtkRenderWindow> renderWindow;
  renderWindow->AddRenderer(leftRenderer);
  renderWindow->AddRenderer(centerRenderer);
  renderWindow->AddRenderer(rightRenderer);
  renderWindow->SetWindowName("DotProduct");
  renderWindow->SetSize(600, 200);

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

  // Add the actor to the scene
  leftRenderer->AddActor(actor1);
  centerRenderer->AddActor(actor2);
  rightRenderer->AddActor(dotProductActor);

  // Render and interact
  renderWindow->Render();
  renderWindowInteractor->Start();

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(DotProduct)

find_package(VTK COMPONENTS 
)

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

Download and Build DotProduct¶

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

cd DotProduct/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:

./DotProduct

WINDOWS USERS

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