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VectorDot

vtk-examples/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).

Question

If you have a question about this example, please use the VTK Discourse Forum

Code

VectorDot.cxx

#include <vtkFloatArray.h>
#include <vtkNew.h>
#include <vtkPointData.h>
#include <vtkPoints.h>
#include <vtkPolyData.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
  vtkNew<vtkPoints> points;
  points->InsertNextPoint(0, 0, 0);
  points->InsertNextPoint(1, 0, 0);
  points->InsertNextPoint(2, 0, 0);

  vtkNew<vtkPolyData> polydata;
  polydata->SetPoints(points);

  // Add normals
  vtkNew<vtkFloatArray> normals;
  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
  vtkNew<vtkFloatArray> vectors;
  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
  vtkNew<vtkVectorDot> vectorDot;
  vectorDot->SetInputData(polydata);
  vectorDot->Update();

  // Get the results
  auto 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.