# DecimatePolyline

VTKExamples/Cxx/PolyData/DecimatePolyline

### Description

This example shows how to [(signal processing)|decimate]]([wikipedia:Decimation) a polyline.

### Code

DecimatePolyline.cxx

    #include <vtkVersion.h>
    #include <vtkDecimatePolylineFilter.h>
    #include <vtkMath.h>
    #include <vtkPolyData.h>
    #include <vtkCellArray.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkProperty.h>

    #include <vtkSmartPointer.h>

    int main(int, char *[])
    {
      const unsigned int numberofpoints = 100;

      vtkPolyData* circle = vtkPolyData::New();
      vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
      vtkSmartPointer<vtkCellArray> lines = vtkSmartPointer<vtkCellArray>::New();
      vtkIdType* lineIndices = new vtkIdType[numberofpoints+1];

      for( unsigned int i = 0; i < numberofpoints; i++ )
      {
        const double angle = 2.0 * vtkMath::Pi() * static_cast< double >( i ) /
          static_cast< double >( numberofpoints );
        points->InsertPoint( static_cast< vtkIdType >( i ),
                             cos( angle ),
                             sin( angle ),
                             0. );
        lineIndices[i] = static_cast< vtkIdType >( i );
      }
      lineIndices[numberofpoints] = 0;
      lines->InsertNextCell( numberofpoints+1, lineIndices );
      delete[] lineIndices;

      circle->SetPoints( points );
      circle->SetLines( lines );

      vtkSmartPointer<vtkPolyDataMapper> c_mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
    #if VTK_MAJOR_VERSION <= 5
      c_mapper->SetInput( circle );
    #else
      c_mapper->SetInputData( circle );
    #endif

      vtkSmartPointer<vtkActor> c_actor =
        vtkSmartPointer<vtkActor>::New();
      c_actor->SetMapper( c_mapper );

      vtkSmartPointer<vtkDecimatePolylineFilter> decimate =
        vtkSmartPointer<vtkDecimatePolylineFilter>::New();
    #if VTK_MAJOR_VERSION <= 5
      decimate->SetInput( circle );
    #else
      decimate->SetInputData( circle );
    #endif
      decimate->SetTargetReduction( 0.95 );
      decimate->Update();

      vtkSmartPointer<vtkPolyDataMapper> d_mapper =
        vtkSmartPointer<vtkPolyDataMapper>::New();
      d_mapper->SetInputConnection( decimate->GetOutputPort() );

      vtkSmartPointer<vtkActor> d_actor =
        vtkSmartPointer<vtkActor>::New();
      d_actor->SetMapper( d_mapper );
      d_actor->GetProperty()->SetColor( 1., 0. ,0. );

      vtkSmartPointer<vtkRenderer> ren =
        vtkSmartPointer<vtkRenderer>::New();
      ren->AddActor( c_actor );
      ren->AddActor( d_actor );

      vtkSmartPointer<vtkRenderWindow> renwin =
        vtkSmartPointer<vtkRenderWindow>::New();
      renwin->AddRenderer( ren );

      vtkSmartPointer<vtkRenderWindowInteractor> iren =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      iren->SetRenderWindow( renwin );

      renwin->Render();

      iren->Start();

      circle->Delete();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(DecimatePolyline)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(DecimatePolyline MACOSX_BUNDLE DecimatePolyline.cxx)

    target_link_libraries(DecimatePolyline ${VTK_LIBRARIES})

### Download and Build DecimatePolyline

Danger

The generation of tar files has not been ported to the new VTKExamples. Some tarballs may be missing or out-of-date.

Click here to download DecimatePolyline and its CMakeLists.txt file. Once the tarball DecimatePolyline.tar has been downloaded and extracted,

    cd DecimatePolyline/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:

    ./DecimatePolyline

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