# PCAStatistics

VTKExamples/Cxx/Utilities/PCAStatistics

Question

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### Code¶

PCAStatistics.cxx

#include <vtkSmartPointer.h>
#include <vtkDoubleArray.h>
#include <vtkMultiBlockDataSet.h>
#include <vtkPCAStatistics.h>
#include <vtkStringArray.h>
#include <vtkTable.h>

int main(int, char*[])
{
// Each one of these arrays is a single component of
// the data. That is, if you have 3D spatial data (x,y,z)
// you need to construct an array of all the x values,
// an array of all the y values, and an array of all the
// z values.

// Construct a data set of 3 3D points.

// These would be all of your "x" values.
const char m0Name[] = "M0";
vtkSmartPointer<vtkDoubleArray> dataset1Arr =
vtkSmartPointer<vtkDoubleArray>::New();
dataset1Arr->SetNumberOfComponents(1);
dataset1Arr->SetName( m0Name );
dataset1Arr->InsertNextValue(0);
dataset1Arr->InsertNextValue(1);
dataset1Arr->InsertNextValue(0);

// These would be all of your "y" values.
const char m1Name[] = "M1";
vtkSmartPointer<vtkDoubleArray> dataset2Arr =
vtkSmartPointer<vtkDoubleArray>::New();
dataset2Arr->SetNumberOfComponents(1);
dataset2Arr->SetName( m1Name );
dataset2Arr->InsertNextValue(0);
dataset2Arr->InsertNextValue(0);
dataset2Arr->InsertNextValue(1);

// These would be all of your "z" values.
const char m2Name[] = "M2";
vtkSmartPointer<vtkDoubleArray> dataset3Arr =
vtkSmartPointer<vtkDoubleArray>::New();
dataset3Arr->SetNumberOfComponents(1);
dataset3Arr->SetName( m2Name );
dataset3Arr->InsertNextValue(0);
dataset3Arr->InsertNextValue(0);
dataset3Arr->InsertNextValue(0);

vtkSmartPointer<vtkTable> datasetTable =
vtkSmartPointer<vtkTable>::New();

vtkSmartPointer<vtkPCAStatistics> pcaStatistics =
vtkSmartPointer<vtkPCAStatistics>::New();
pcaStatistics->SetInputData( vtkStatisticsAlgorithm::INPUT_DATA, datasetTable );
pcaStatistics->SetColumnStatus("M0", 1 );
pcaStatistics->SetColumnStatus("M1", 1 );
pcaStatistics->SetColumnStatus("M2", 1 );
pcaStatistics->RequestSelectedColumns();
pcaStatistics->SetDeriveOption(true);
pcaStatistics->Update();

///////// Eigenvalues ////////////
vtkSmartPointer<vtkDoubleArray> eigenvalues =
vtkSmartPointer<vtkDoubleArray>::New();
pcaStatistics->GetEigenvalues(eigenvalues);
//  double eigenvaluesGroundTruth[3] = {.5, .166667, 0};
for(vtkIdType i = 0; i < eigenvalues->GetNumberOfTuples(); i++)
{
std::cout << "Eigenvalue " << i << " = " << eigenvalues->GetValue(i) << std::endl;
}

///////// Eigenvectors ////////////
vtkSmartPointer<vtkDoubleArray> eigenvectors =
vtkSmartPointer<vtkDoubleArray>::New();

pcaStatistics->GetEigenvectors(eigenvectors);
for(vtkIdType i = 0; i < eigenvectors->GetNumberOfTuples(); i++)
{
std::cout << "Eigenvector " << i << " : ";
double* evec = new double[eigenvectors->GetNumberOfComponents()];
eigenvectors->GetTuple(i, evec);
for(vtkIdType j = 0; j < eigenvectors->GetNumberOfComponents(); j++)
{
std::cout << evec[j] << " ";
vtkSmartPointer<vtkDoubleArray> eigenvectorSingle =
vtkSmartPointer<vtkDoubleArray>::New();
pcaStatistics->GetEigenvector(i, eigenvectorSingle);
}
delete[] evec;
std::cout << std::endl;
}

return EXIT_SUCCESS;
}


### CMakeLists.txt¶

cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

project(PCAStatistics)

find_package(VTK COMPONENTS
vtkCommonCore
vtkCommonDataModel
if (NOT VTK_FOUND)
message("Skipping PCAStatistics: ${VTK_NOT_FOUND_MESSAGE}") return () endif() message (STATUS "VTK_VERSION:${VTK_VERSION}")
if (VTK_VERSION VERSION_LESS "8.90.0")
# old system
include(${VTK_USE_FILE}) add_executable(PCAStatistics MACOSX_BUNDLE PCAStatistics.cxx ) target_link_libraries(PCAStatistics PRIVATE${VTK_LIBRARIES})
else ()
# include all components
add_executable(PCAStatistics MACOSX_BUNDLE PCAStatistics.cxx )
target_link_libraries(PCAStatistics PRIVATE ${VTK_LIBRARIES}) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS PCAStatistics MODULES${VTK_LIBRARIES}
)
endif ()


cd PCAStatistics/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:

./PCAStatistics


WINDOWS USERS

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