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 = dynamic_cast<vtkFloatArray*> ( 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.