# DotProduct

VTKExamples/Cxx/Images/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.

### Code

DotProduct.cxx

    #include <vtkSmartPointer.h>
    #include <vtkImageMathematics.h>
    #include <vtkImageCast.h>
    #include <vtkImageMapper3D.h>
    #include <vtkImageActor.h>
    #include <vtkPointData.h>
    #include <vtkImageData.h>
    #include <vtkImageCanvasSource2D.h>
    #include <vtkImageDotProduct.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkGlyph3DMapper.h>
    #include <vtkArrowSource.h>
    #include <vtkXMLImageDataWriter.h>

    int main(int, char *[])
    {
      // Create an image
      vtkSmartPointer<vtkImageData> image1 =
        vtkSmartPointer<vtkImageData>::New();
      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;

      vtkSmartPointer<vtkXMLImageDataWriter> writer =
        vtkSmartPointer<vtkXMLImageDataWriter>::New();
      writer->SetInputData(image1);
      writer->SetFileName("test.vti");
      writer->Write();

      // Create another image
      vtkSmartPointer<vtkImageData> image2 =
        vtkSmartPointer<vtkImageData>::New();
      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
      vtkSmartPointer<vtkImageDotProduct> dotProductFilter =
        vtkSmartPointer<vtkImageDotProduct>::New();
      dotProductFilter->SetInput1Data(image1);
      dotProductFilter->SetInput2Data(image2);
      dotProductFilter->Update();
      std::cout << "output is of type: " << dotProductFilter->GetOutput()->GetScalarTypeAsString() << std::endl;

      vtkSmartPointer<vtkImageMathematics> imageMath =
        vtkSmartPointer<vtkImageMathematics>::New();
      imageMath->SetOperationToMultiplyByK();
      imageMath->SetConstantK(255.0);
      imageMath->SetInputConnection(dotProductFilter->GetOutputPort());
      imageMath->Update();

      vtkSmartPointer<vtkImageCast> imageCast =
        vtkSmartPointer<vtkImageCast>::New();
      imageCast->SetOutputScalarTypeToUnsignedChar();
      imageCast->SetInputConnection(imageMath->GetOutputPort());
      imageCast->Update();

      vtkSmartPointer<vtkImageActor> dotProductActor =
        vtkSmartPointer<vtkImageActor>::New();
      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");

      vtkSmartPointer<vtkArrowSource> arrowSource =
        vtkSmartPointer<vtkArrowSource>::New();

      vtkSmartPointer<vtkGlyph3DMapper> glyph3Dmapper1 =
        vtkSmartPointer<vtkGlyph3DMapper>::New();
      glyph3Dmapper1->SetSourceConnection(arrowSource->GetOutputPort());
      glyph3Dmapper1->SetInputData(image1);
      glyph3Dmapper1->Update();

      vtkSmartPointer<vtkActor> actor1 =
        vtkSmartPointer<vtkActor>::New();
      actor1->SetMapper(glyph3Dmapper1);

      vtkSmartPointer<vtkGlyph3DMapper> glyph3Dmapper2 =
        vtkSmartPointer<vtkGlyph3DMapper>::New();
      glyph3Dmapper2->SetSourceConnection(arrowSource->GetOutputPort());
      glyph3Dmapper2->SetInputData(image2);
      glyph3Dmapper2->Update();

      vtkSmartPointer<vtkActor> actor2 =
        vtkSmartPointer<vtkActor>::New();
      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
      vtkSmartPointer<vtkRenderer> leftRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      leftRenderer->SetViewport(leftViewport);

      vtkSmartPointer<vtkRenderer> centerRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      centerRenderer->SetViewport(centerViewport);

      vtkSmartPointer<vtkRenderer> rightRenderer =
        vtkSmartPointer<vtkRenderer>::New();
      rightRenderer->SetViewport(rightViewport);

      vtkSmartPointer<vtkRenderWindow> renderWindow =
        vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(leftRenderer);
      renderWindow->AddRenderer(centerRenderer);
      renderWindow->AddRenderer(rightRenderer);

      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      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 3.3 FATAL_ERROR)

    project(DotProduct)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersSources
      vtkIOXML
      vtkImagingCore
      vtkImagingMath
      vtkImagingSources
      vtkInteractionStyle
      vtkRenderingCore
      vtkRenderingFreeType
      vtkRenderingOpenGL2 QUIET)
    if (NOT VTK_FOUND)
      message("Skipping DotProduct: ${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(DotProduct MACOSX_BUNDLE DotProduct.cxx )
      target_link_libraries(DotProduct PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      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}
        )
    endif ()

### 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.