# VectorDot

VTKExamples/Cxx/Math/VectorDot

### Description

Note that the filter maps the values to a scalar range. In the example, the values of the dot products are

     1, .707, 0

The filter outputs

     1, .414, -1

because the default scalar range that the filter maps the values to is (-1,1).

### Code

VectorDot.cxx

    #include <vtkSmartPointer.h>
    #include <vtkPoints.h>
    #include <vtkPolyData.h>
    #include <vtkFloatArray.h>
    #include <vtkPointData.h>
    #include <vtkVectorDot.h>

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

    int main(int, char *[])
    {
      // Generate data
      vtkSmartPointer<vtkPoints> points =
        vtkSmartPointer<vtkPoints>::New();
      points->InsertNextPoint(0,0,0);
      points->InsertNextPoint(1,0,0);
      points->InsertNextPoint(2,0,0);

      vtkSmartPointer<vtkPolyData> polydata =
        vtkSmartPointer<vtkPolyData>::New();
      polydata->SetPoints(points);

      // Add normals
      vtkSmartPointer<vtkFloatArray> normals =
        vtkSmartPointer<vtkFloatArray>::New();
      normals->SetNumberOfComponents(3);
      normals->SetName("Normals");

      float n0[3] = {1,0,0};
      float n1[3] = {1,0,0};
      float n2[3] = {1,0,0};
      normals->InsertNextTupleValue(n0);
      normals->InsertNextTupleValue(n1);
      normals->InsertNextTupleValue(n2);

      polydata->GetPointData()->SetNormals(normals);

      // Add vectors
      vtkSmartPointer<vtkFloatArray> vectors =
        vtkSmartPointer<vtkFloatArray>::New();
      vectors->SetNumberOfComponents(3);
      vectors->SetName("Vectors");

      float v0[3] = {1,0,0};
      float v1[3] = {.707f,.707f,0};
      float v2[3] = {0,1,0};
      vectors->InsertNextTupleValue(v0);
      vectors->InsertNextTupleValue(v1);
      vectors->InsertNextTupleValue(v2);

      polydata->GetPointData()->SetVectors(vectors);

      // Compute the dot products between normals and vectors
      vtkSmartPointer<vtkVectorDot> vectorDot =
          vtkSmartPointer<vtkVectorDot>::New();
      vectorDot->SetInputData(polydata);
      vectorDot->Update();

      // Get the results
      vtkFloatArray* scalars = vtkFloatArray::SafeDownCast ( vectorDot->GetOutput()->GetPointData()->GetScalars() );

      // Output the results
      for(vtkIdType i = 0; i < scalars->GetNumberOfTuples(); i++)
      {
        std::cout << "Value " << i << " : " << scalars->GetValue(i) << std::endl;
      }

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(VectorDot)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkFiltersCore QUIET)
    if (NOT VTK_FOUND)
      message("Skipping VectorDot: ${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(VectorDot MACOSX_BUNDLE VectorDot.cxx )
      target_link_libraries(VectorDot PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(VectorDot MACOSX_BUNDLE VectorDot.cxx )
      target_link_libraries(VectorDot PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS VectorDot
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build VectorDot

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

    cd VectorDot/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:

    ./VectorDot

WINDOWS USERS

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