### Description¶

The algorithm used is the one described by Peter Lindstrom in his Siggraph 2000 paper, "Out-of-Core Simplification of Large Polygonal Models." The general approach of the algorithm is to cluster vertices in a uniform binning of space, accumulating the quadric of each triangle (pushed out to the triangles vertices) within each bin, and then determining an optimal position for a single vertex in a bin by using the accumulated quadric.

Seealso

Other languages

See (CSharp)

Question

### Code¶

#include <vtkCamera.h>
#include <vtkNamedColors.h>
#include <vtkNew.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkProperty.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkSmartPointer.h>
#include <vtkSphereSource.h>

int main(int argc, char* argv[])
{
vtkSmartPointer<vtkPolyData> inputPolyData;
if (argc > 1)
{
}
else
{
vtkNew<vtkSphereSource> sphereSource;
sphereSource->SetThetaResolution(30);
sphereSource->SetPhiResolution(15);
sphereSource->Update();
inputPolyData = sphereSource->GetOutput();
}

vtkNew<vtkNamedColors> colors;

std::cout << "Before decimation" << std::endl << "------------" << std::endl;
std::cout << "There are " << inputPolyData->GetNumberOfPoints() << " points."
<< std::endl;
std::cout << "There are " << inputPolyData->GetNumberOfPolys() << " polygons."
<< std::endl;

decimate->SetInputData(inputPolyData);
decimate->UseFeatureEdgesOn();
decimate->Update();

vtkNew<vtkPolyData> decimated;
decimated->ShallowCopy(decimate->GetOutput());

std::cout << "After decimation" << std::endl << "------------" << std::endl;
std::cout << "There are " << decimated->GetNumberOfPoints() << " points."
<< std::endl;
std::cout << "There are " << decimated->GetNumberOfPolys() << " polygons."
<< std::endl;
std::cout << "Reduction: "
<< static_cast<double>((inputPolyData->GetNumberOfPolys() -
decimated->GetNumberOfPolys())) /
static_cast<double>(inputPolyData->GetNumberOfPolys())
<< std::endl;

vtkNew<vtkPolyDataMapper> inputMapper;
inputMapper->SetInputData(inputPolyData);

vtkNew<vtkProperty> backFace;
backFace->SetColor(colors->GetColor3d("Gold").GetData());

vtkNew<vtkActor> inputActor;
inputActor->SetMapper(inputMapper);
inputActor->GetProperty()->SetInterpolationToFlat();
inputActor->GetProperty()->SetColor(
colors->GetColor3d("NavajoWhite").GetData());
inputActor->SetBackfaceProperty(backFace);

vtkNew<vtkPolyDataMapper> decimatedMapper;
decimatedMapper->SetInputData(decimated);

vtkNew<vtkActor> decimatedActor;
decimatedActor->SetMapper(decimatedMapper);
decimatedActor->GetProperty()->SetColor(
colors->GetColor3d("NavajoWhite").GetData());
decimatedActor->GetProperty()->SetInterpolationToFlat();
decimatedActor->SetBackfaceProperty(backFace);

// There will be one render window
vtkNew<vtkRenderWindow> renderWindow;
renderWindow->SetSize(600, 300);

// And one interactor
vtkNew<vtkRenderWindowInteractor> interactor;
interactor->SetRenderWindow(renderWindow);

// Define viewport ranges
// (xmin, ymin, xmax, ymax)
double leftViewport[4] = {0.0, 0.0, 0.5, 1.0};
double rightViewport[4] = {0.5, 0.0, 1.0, 1.0};

// Setup both renderers
vtkNew<vtkRenderer> leftRenderer;
leftRenderer->SetViewport(leftViewport);
leftRenderer->SetBackground(colors->GetColor3d("Peru").GetData());

vtkNew<vtkRenderer> rightRenderer;
rightRenderer->SetViewport(rightViewport);
rightRenderer->SetBackground(colors->GetColor3d("CornflowerBlue").GetData());

// Add the sphere to the left and the cube to the right

// Shared camera looking down the -y axis
vtkNew<vtkCamera> camera;
camera->SetPosition(0, -1, 0);
camera->SetFocalPoint(0, 0, 0);
camera->SetViewUp(0, 0, 1);
camera->Elevation(30);
camera->Azimuth(30);

leftRenderer->SetActiveCamera(camera);
rightRenderer->SetActiveCamera(camera);

leftRenderer->ResetCamera();
leftRenderer->ResetCameraClippingRange();

renderWindow->Render();
interactor->Start();

return EXIT_SUCCESS;
}


### CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

find_package(VTK COMPONENTS
CommonColor
CommonCore
CommonDataModel
FiltersCore
IOXML
InteractionStyle
RenderingContextOpenGL2
RenderingCore
RenderingFreeType
RenderingGL2PSOpenGL2
RenderingOpenGL2
)

if (NOT VTK_FOUND)
message(FATAL_ERROR "QuadricClustering: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
target_link_libraries(QuadricClustering PRIVATE ${VTK_LIBRARIES} ) # vtk_module_autoinit is needed vtk_module_autoinit( TARGETS QuadricClustering MODULES${VTK_LIBRARIES}
)


cd QuadricClustering/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:

./QuadricClustering


WINDOWS USERS

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