What Does The vtkImageData Looks Like

What does the vtkImageData look like? It has a multi-layered point set. In the following example, I show all points in a vtkImageData object in the left reader and its polydata in the right render.

#define vtkSPtr vtkSmartPointer
#define vtkSPtrNew(Var, Type) vtkSPtr<Type> Var = vtkSPtr<Type>::New();

unsigned char inval = 255;
unsigned char outval = 0;
double spacingVal = 0.5;

vtkSPtr<vtkImageData> ConvertPolydataToImage(vtkPolyData *polydata)
{
    double spacingVal = 2;
    double bounds[6];
    polydata->GetBounds(bounds);

    int dim[3];
    for (int i = 0; i < 3; i++)
    {
        dim[i] = static_cast<int>( ceil((bounds[2 * i + 1] - bounds[2 * i]) / spacingVal) );
    }
    double origin[3];
    origin[0] = bounds[0] + spacingVal / 2;
    origin[1] = bounds[2] + spacingVal / 2;
    origin[2] = bounds[4] + spacingVal / 2;

    vtkSPtrNew(imageData, vtkImageData)
    imageData->SetSpacing(spacingVal, spacingVal, spacingVal);
    imageData->SetDimensions(dim);
    imageData->SetOrigin(origin);
    imageData->AllocateScalars(VTK_UNSIGNED_CHAR, 1);
    imageData->SetExtent( 0, dim[0] - 1, 0, dim[1] - 1, 0, dim[2] - 1 );

    // fill the imageData with foreground voxels
    vtkIdType count = imageData->GetNumberOfPoints();
    for (vtkIdType i = 0; i < count; ++i)
    {
        imageData->GetPointData()->GetScalars()->SetTuple1(i, inval);
    }

    // polygonal data --> imageData stencil:
    vtkSPtrNew(pd2stenc, vtkPolyDataToImageStencil);
    pd2stenc->SetInputData(polydata);
    pd2stenc->SetOutputOrigin(origin);
    pd2stenc->SetOutputSpacing(spacingVal, spacingVal, spacingVal);
    pd2stenc->SetOutputWholeExtent(imageData->GetExtent());
    pd2stenc->Update();

    // cut the corresponding white imageData and set the background:
    vtkSPtrNew(imgstenc, vtkImageStencil);
    imgstenc->SetInputData(imageData);
    imgstenc->SetStencilConnection(pd2stenc->GetOutputPort());
    imgstenc->ReverseStencilOff();
    imgstenc->SetBackgroundValue( outval );
    imgstenc->Update();

    imageData->DeepCopy(imgstenc->GetOutput());
    return imageData;
}

int main(int, char *[])
{
    setbuf( stdout, nullptr );

    vtkSPtrNew( sphereSource, vtkSphereSource );
    sphereSource->SetRadius(20);
    sphereSource->SetPhiResolution(10);
    sphereSource->SetThetaResolution(10);
    sphereSource->Update();
    vtkSPtr<vtkPolyData> spherePd = sphereSource->GetOutput();

    vtkSPtr<vtkImageData> sphereImage = ConvertPolydataToImage( spherePd );
    // ============= start to show image data ===================
    vtkSPtrNew( spheres, vtkAppendPolyData );
    cout << "spherePd->GetNumberOfPoints(): " << sphereImage->GetNumberOfPoints() << endl;
    for( int i = 0; i < sphereImage->GetNumberOfPoints(); ++i )
    {
        PointStruct pt( sphereImage->GetPoint( i ) );
        vtkSPtrNew( tmpSphere, vtkSphereSource );
        tmpSphere->SetCenter( pt.point );
        tmpSphere->SetRadius( 0.1 );
        tmpSphere->Update();

        spheres->AddInputData( tmpSphere->GetOutput() );
    }
    spheres->Update();

    vtkSPtrNew( sphereMapper, vtkPolyDataMapper );
    sphereMapper->SetInputData( spheres->GetOutput() );
    sphereMapper->Update();
    vtkSPtrNew( sphereActor, vtkActor );
    sphereActor->SetMapper( sphereMapper );
    sphereActor->GetProperty()->SetColor( 0, 1, 0 );
    // ============= Finish: show image data ===================

    // ============== convert image ===============
    vtkSPtrNew( marchingCubes, vtkImageMarchingCubes );
    marchingCubes->SetInputData( sphereImage );
    marchingCubes->SetValue( 0, (inval + outval)/2 );
    marchingCubes->SetNumberOfContours( 1 );
    marchingCubes->Update();

    // Fill the holes
    auto fillHoles = vtkSmartPointer<vtkFillHolesFilter>::New();
    fillHoles->SetInputConnection( marchingCubes->GetOutputPort() );
    fillHoles->SetHoleSize(1000.0);

    // Make the triangle winding order consistent
    auto normals = vtkSmartPointer<vtkPolyDataNormals>::New();
    normals->SetInputConnection(fillHoles->GetOutputPort());
    normals->ConsistencyOn();
    normals->SplittingOff();
    normals->GetOutput()->GetPointData()->SetNormals(
        marchingCubes->GetOutput()->GetPointData()->GetNormals());
    normals->Update();
    // ==============finished: convert image ===============

    vtkSPtrNew( imageMapper, vtkPolyDataMapper );
    imageMapper->SetInputData( normals->GetOutput() );
    imageMapper->Update();

    vtkSPtrNew( imageActor, vtkActor );
    imageActor->SetMapper( imageMapper );

    double leftViewport[4] = {0.0, 0.0, 0.5, 1.0};
    double rightViewport[4] = {0.5, 0.0, 1.0, 1.0};

    // Setup renderers
    vtkSPtrNew( leftRenderer, vtkRenderer );
    leftRenderer->SetViewport( leftViewport );
    leftRenderer->AddActor( sphereActor );
    leftRenderer->SetBackground(.6, .5, .4);
    leftRenderer->ResetCamera();

    vtkSPtrNew( rightRenderer, vtkRenderer );
    rightRenderer->SetViewport(rightViewport);
    rightRenderer->AddActor( imageActor );
    rightRenderer->SetBackground(.4, .5, .6);
    rightRenderer->ResetCamera();

    // Setup render window
    vtkSPtrNew( renderWindow, vtkRenderWindow );
    renderWindow->AddRenderer( leftRenderer );
    renderWindow->AddRenderer( rightRenderer );
    renderWindow->SetSize( 900, 300 );

    // Setup render window interactor
    vtkSPtrNew( renderWindowInteractor, vtkRenderWindowInteractor );

    // Render and start interaction
    renderWindowInteractor->SetRenderWindow(renderWindow);
    renderWindowInteractor->Start();

    return EXIT_SUCCESS;
}

Header files in the project:

#include <vtkVersion.h>
#include <vtkImageData.h>
#include <vtkImageMapper3D.h>
#include <vtkImageStencil.h>
#include <vtkImageStencilData.h>
#include <vtkImageToImageStencil.h>
#include <vtkJPEGReader.h>
#include <vtkPointData.h>
#include <vtkSmartPointer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkInteractorStyleImage.h>
#include <vtkRenderer.h>
#include <vtkImageActor.h>
#include <vtkPolyDataToImageStencil.h>
#include <vtkPolyData.h>
#include <vtkSTLReader.h>
#include <vtkProperty.h>
#include <vtkImageProperty.h>
#include <vtkSphereSource.h>
#include <vtkPolyDataMapper.h>
#include <vtkImageDataGeometryFilter.h>
#include <vtkImageMarchingCubes.h>
#include <vtkPolyDataNormals.h>
#include <vtkFillHolesFilter.h>
#include <vtkCleanPolyData.h>
#include <vtkTriangleFilter.h>
#include <vtkAppendPolyData.h>
#include <vtkImageMarchingCubes.h>
#include <vtkImageWeightedSum.h>
#include <vtkConeSource.h>
#include <vtkPolyDataConnectivityFilter.h>

#include "../share/tool.h"