# DotProduct

Repository source: 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

### 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->SetWindowName("DotProduct");
renderWindow->SetSize(600, 200);

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

// Add the actor to the scene

// 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
CommonColor
CommonCore
CommonDataModel
ImagingCore
ImagingMath
InteractionStyle
RenderingContextOpenGL2
RenderingCore
RenderingFreeType
RenderingGL2PSOpenGL2
RenderingOpenGL2
)

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.")
target_link_libraries(DotProduct PRIVATE ${VTK_LIBRARIES} ) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS DotProduct MODULES${VTK_LIBRARIES}
)

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.