[vtkusers] vtkImplicitFunction question

[alex dowson]

Hi
I am trying to do tricky part as match implicit surface with parametric surface but not getting proper result.
First I create implicit surface using vtkPlane->vtkSampleFunction and create parametric surface using vtkPlaneSource. Then apply transformation to both as rotate 20 degree in x and rotate 30 degree in Y. Both output should be similar but it’s different. I am not able to figure out reason. 
As you can see in picture red plane is produced using vtkSampleFunction and white one is using vtkPlaneSource.
I attached screen shot and code if any one can explain me why it is different.
code
#include "vtkSmartPointer.h"
#include "vtkRenderer.h"
#include "vtkRenderWindow.h"
#include "vtkRenderWindowInteractor.h"
#include "vtkInteractorStyleTrackballCamera.h"
#include "vtkPolyDataMapper.h"
#include "vtkActor.h"
#include "vtkContourFilter.h"
#include "vtkSampleFunction.h"
#include "vtkPlane.h"
#include "vtkProperty.h"
#include "vtkTransformPolyDataFilter.h"
#include "vtkTransform.h"
#include "vtkOutlineFilter.h"
#include "vtkPlaneSource.h"


int main()
{


    vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();


    vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
    renderWindow->SetSize(640,480);
    renderWindow->AddRenderer(renderer);


    vtkSmartPointer<vtkRenderWindowInteractor> renderInteractor =     vtkSmartPointer<vtkRenderWindowInteractor>::New();
    renderInteractor->SetRenderWindow(renderWindow);


    vtkSmartPointer< vtkInteractorStyleTrackballCamera> style = vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
    renderInteractor->SetInteractorStyle(style);


    vtkSmartPointer<vtkTransform> xform = vtkSmartPointer<vtkTransform>::New();
    xform->Identity();
    xform->RotateX(20);
    xform->RotateY(30);





    vtkSmartPointer<vtkPlane> plane = vtkSmartPointer<vtkPlane>::New();
    plane->SetNormal(1,0,0);
    plane->SetTransform(xform);


    // Sample the function
    vtkSmartPointer<vtkSampleFunction> sample = vtkSmartPointer<vtkSampleFunction>::New();
    sample->SetSampleDimensions(10,10,10);
    sample->SetImplicitFunction(plane);
    double xmin = -0.5, xmax=0.5, ymin=-0.5, ymax=0.5, zmin=-0.5, zmax=0.5;
    sample->SetModelBounds(xmin, xmax, ymin, ymax, zmin, zmax);

    
    // Create the 0 isosurface
    vtkSmartPointer<vtkContourFilter> contours =     vtkSmartPointer<vtkContourFilter>::New();
    contours->SetInputConnection(sample->GetOutputPort());
    contours->SetValue(0,0);
    contours->Update();



    vtkSmartPointer<vtkPolyDataMapper> mapperSample = vtkSmartPointer<vtkPolyDataMapper>::New();
    mapperSample->SetInputConnection(contours->GetOutputPort());


    vtkSmartPointer<vtkActor> actorSample = vtkSmartPointer<vtkActor>::New();
    actorSample->SetMapper(mapperSample);

    renderer->AddActor(actorSample);


    vtkSmartPointer<vtkPlaneSource> planeSource = vtkSmartPointer<vtkPlaneSource>::New();
    planeSource->SetNormal(1,0,0);


    vtkSmartPointer<vtkTransformPolyDataFilter> xformFilter = 
        vtkSmartPointer<vtkTransformPolyDataFilter>::New();
    xformFilter->SetInput(planeSource->GetOutput());
    xformFilter->SetTransform(xform);


    vtkSmartPointer<vtkPolyDataMapper> xformMapper= vtkSmartPointer<vtkPolyDataMapper>::New();
    xformMapper->SetInput(xformFilter->GetOutput());


    vtkSmartPointer<vtkActor> xformActor = vtkSmartPointer<vtkActor>::New();
    xformActor->SetMapper(xformMapper);


    renderer->AddActor(xformActor);


    // create outline
    vtkSmartPointer<vtkOutlineFilter> outline = vtkSmartPointer<vtkOutlineFilter>::New();
    outline->SetInputConnection(xformFilter->GetOutputPort());

    // map it to graphics primitives
    vtkSmartPointer<vtkPolyDataMapper> outlineMapper = vtkSmartPointer<vtkPolyDataMapper>::New();
    outlineMapper->SetInputConnection(outline->GetOutputPort());

    // create an actor for it
    vtkSmartPointer<vtkActor> outlineActor = vtkSmartPointer<vtkActor>::New();
    outlineActor->SetMapper(outlineMapper);
    outlineActor->GetProperty()->SetColor(0,0,0);


    renderer->AddActor(outlineActor);



    renderer->SetBackground(.1,.2,.3);    
    renderer->ResetCamera();
    renderWindow->Render();


    renderInteractor->Start();


    return EXIT_SUCCESS;
}
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