# 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).

Question

### 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);

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);

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
target_link_libraries(VectorDot PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS VectorDot MODULES${VTK_LIBRARIES}
)
endif ()


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.