# vtkSplineWidget(2) vtkMarchingSquares and vtkImageData

**URL:** https://discourse.vtk.org/t/vtksplinewidget-2-vtkmarchingsquares-and-vtkimagedata/464
**Category:** Support
**Created:** [March 12, 2019, 6:21pm UTC](https://discourse.vtk.org/t/vtksplinewidget-2-vtkmarchingsquares-and-vtkimagedata/464 "2019-03-12T18:21:02Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![Romain](https://discourse.vtk.org/user_avatar/discourse.vtk.org/romain/32/32_2.png) [@Romain](https://discourse.vtk.org/u/Romain)
#### Post date: [March 12, 2019, 6:21pm UTC](https://discourse.vtk.org/t/vtksplinewidget-2-vtkmarchingsquares-and-vtkimagedata/464/1 "2019-03-12T18:21:02Z")

</div>

Hello everyone,

I’m working with vtk 8.2 on Windows 10 with VS 2017.

I try to create a closed Spline around the contour of a binary image in purpose to change the value of each pixels inside the closed spline.  
To do this, I use vtkMarchingSquares to extract the contour of the binary image.  
After that, I try to put the points from the output polydata of the vtkMarchingSquares but the spline is not set at the expected position.

I’m not sure what I did wrong. Maybe there is too much points on the contour?

```
#include <vtkRenderWindow.h>
#include <vtkRenderer.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkSmartPointer.h>
#include <vtkSplineWidget2.h>
#include <vtkSplineWidget.h>
#include <vtkCardinalSpline.h>
#include <vtkKochanekSpline.h>
#include <vtkParametricSpline.h>
#include <vtkImageData.h>
#include <vtkPointData.h>
#include <vtkDataSetMapper.h>
#include <vtkProperty.h>
#include <vtkImageActor.h>
#include <vtkContourFilter.h>
#include <vtkPolyData.h>
#include <vtkCellData.h>
#include <vtkDataArray.h>
#include <vtkCellArray.h>
#include <vtkPolyDataMapper.h>
#include <vtkMarchingSquares.h>
#include <vtkImageStack.h>
#include <vtkSplineRepresentation.h>

int main(int, char *[])
{
	vtkNew<vtkImageData> image;
	image->SetDimensions(512, 512, 2);
	image->SetOrigin(0, 0, 0);
	image->SetSpacing(0.97, 0.97, 1);
	image->AllocateScalars(VTK_SHORT, 1);
	for (int k = 0; k < 2; ++k)
	{
		for (int j = 0; j < 512; ++j)
		{
			for (int i = 0; i < 512; ++i)
			{
				short * pixel = static_cast<short *>(image->GetScalarPointer(i, j, k));
				if (i > 100 && i < 300 && j > 100 && j < 300)
				{
					pixel[0] = 255;
				}
				else
				{
					pixel[0] = 0;
				}
			}
		}
	}

	vtkNew<vtkMarchingSquares> contourFilter;
	contourFilter->SetInputData(image);
	contourFilter->GenerateValues(1, 255, 255);
	contourFilter->Update();
	vtkSmartPointer<vtkPolyData> contourPolyData = contourFilter->GetOutput();

	//	vtkNew<vtkDataSetMapper> imageMapper;
	//	imageMapper->SetInputData(image);
	vtkNew<vtkImageActor> imageActor;
	imageActor->SetInputData(image);

	vtkNew<vtkPolyDataMapper> contourMapper;
	contourMapper->SetInputData(contourPolyData);
	vtkNew<vtkActor> contourActor;
	contourActor->SetMapper(contourMapper);
	contourActor->GetProperty()->SetLineWidth(2);
	contourActor->GetProperty()->SetColor(1, 0, 0);

	// A renderer and render window
	vtkSmartPointer<vtkRenderer> renderer =
			vtkSmartPointer<vtkRenderer>::New();
	vtkSmartPointer<vtkRenderWindow> renderWindow =
			vtkSmartPointer<vtkRenderWindow>::New();
	renderWindow->AddRenderer(renderer);

	// An interactor
	vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
			vtkSmartPointer<vtkRenderWindowInteractor>::New();
	renderWindowInteractor->SetRenderWindow(renderWindow);

	vtkNew<vtkParametricSpline> parametricSpline;
	parametricSpline->SetPoints(contourPolyData->GetPoints());

	vtkNew<vtkSplineRepresentation> splineRepresentation;
	splineRepresentation->SetParametricSpline(parametricSpline);
	vtkNew<vtkKochanekSpline> xSpline;
	vtkNew<vtkKochanekSpline> ySpline;
	vtkNew<vtkKochanekSpline> zSpline;
	splineRepresentation->GetParametricSpline()->SetXSpline(xSpline);
	splineRepresentation->GetParametricSpline()->SetYSpline(ySpline);
	splineRepresentation->GetParametricSpline()->SetZSpline(zSpline);
	splineRepresentation->GetParametricSpline()->SetPoints(contourPolyData->GetPoints());
	splineRepresentation->ClosedOn();

	vtkSmartPointer<vtkSplineWidget2> splineWidget =
			vtkSmartPointer<vtkSplineWidget2>::New();
	splineWidget->SetRepresentation(splineRepresentation);
	splineWidget->SetInteractor(renderWindowInteractor);

	renderWindowInteractor->Initialize();
	renderWindow->Render();
	splineWidget->On();
	renderer->AddActor(imageActor);
	renderer->ResetCamera();
	renderWindowInteractor->Start();

	return EXIT_SUCCESS;
}
```

---

<div class="post-metadata">

### Author: ![Romain](https://discourse.vtk.org/user_avatar/discourse.vtk.org/romain/32/32_2.png) [@Romain](https://discourse.vtk.org/u/Romain)
#### Post date: [March 14, 2019, 8:22am UTC](https://discourse.vtk.org/t/vtksplinewidget-2-vtkmarchingsquares-and-vtkimagedata/464/2 "2019-03-14T08:22:58Z")

</div>

Hi everyone,

I really don’t understand the behavior of vtkSplineWidget and vtkSplineWidget2.  
I do some tests like this:

I create a vtkParametricSpline with the same points that represents a square:

> vtkNew\<vtkPoints\> points;  
> points-\>InsertNextPoint(0.97, 0.97, 0);  
> points-\>InsertNextPoint(0.97, 1.94, 0);  
> points-\>InsertNextPoint(0.97, 2.91, 0);  
> points-\>InsertNextPoint(1.94, 2.91, 0);  
> points-\>InsertNextPoint(2.91, 2.91, 0);  
> points-\>InsertNextPoint(2.91, 1.94, 0);  
> points-\>InsertNextPoint(2.91, 0.97, 0);  
> points-\>InsertNextPoint(1.94, 0.97, 0);  
> vtkNew\<vtkParametricSpline\> spline;  
> spline-\>SetPoints(edgeCoords);  
> spline-\>ClosedOn();

Once I display this spline using vtkSplineWidget:

> vtkNew\<vtkSplineWidget\> splineWidget;  
> splineWidget-\>SetParametricSpline(spline);  
> splineWidget-\>SetInteractor(renderWindowInteractor);

I obtain this result:

![vtkSplineWidget](https://discourse.vtk.org/uploads/default/original/1X/b60cf7e72212809d3731a258483a8b076f9c2683.png)

Once I display the same spline using vtkSplineWidget2:

> vtkNew\<vtkSplineWidget2\> splineWidget;  
> vtkNew\<vtkSplineRepresentation\> splineRepresentation;  
> splineRepresentation-\>SetParametricSpline(spline);  
> splineWidget-\>SetRepresentation(splineRepresentation);  
> splineWidget-\>SetInteractor(renderWindowInteractor);

I obtain this:

![vtkSplineWidget2](https://discourse.vtk.org/uploads/default/original/1X/85aa7046929f495959474338d0bb95825072d6d6.png)

And finally when I put the spline inside a vtkParametricFunctionSource and display it using a vtkPolydataMapper/vtkActor:

> vtkNew\<vtkParametricFunctionSource\> functionSource;  
> functionSource-\>SetParametricFunction(spline);  
> functionSource-\>Update();  
> vtkNew\<vtkPolyDataMapper\> splineMapper;  
> splineMapper-\>SetInputConnection(functionSource-\>GetOutputPort());  
> vtkNew\<vtkActor\> splineActor;  
> splineActor-\>SetMapper(splineMapper);  
> splineActor-\>GetProperty()-\>SetLineWidth(2.0f);  
> splineActor-\>GetProperty()-\>SetColor(1.0, 0.0, 0.0);

I obtain the expected result:

![vtkParametricFunctionSource](https://discourse.vtk.org/uploads/default/original/1X/27ecefdf9086326ab9dedb56a2def16e82b35d22.png)

I really don’t understand what I did wrong using the vtkSplineWidget\* object to not obtain the same result.

I read the documentation of those two widgets but I found nothing that can explain this behavior.