[vtkusers] vtkLoopSubdivisionFilter displays incorrect shape

[madz]

I have a 3d surface plot which looks like the following image.
<http://vtk.1045678.n5.nabble.com/file/n5724631/not_smooth.png> 

To give the image a more smoother interpolated look I applied the
vtkLoopSubdivisionFilter. However, after applying the filter, the shape of
the grid looks greatly altered. 
E.g - The highest peak which was around 3 was lowered to 2.5 while the
lowest went from 0 to 0.5 etc..
The altered pic looks like the following,

<http://vtk.1045678.n5.nabble.com/file/n5724631/loopdiv.png> 

How do I remedy this, it's important that the grid displays the correct
values. The simplified code;

#include <vtkSmartPointer.h>
#include <vtkActor.h>
#include <vtkDelaunay2D.h>
#include <vtkLookupTable.h>
#include <vtkMath.h>
#include <vtkPoints.h>
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkRenderer.h>
#include <vtkCubeAxesActor.h>
#include <vtkInteractorStyleTrackballCamera.h>
#include <vtkCamera.h>
#include <vtkLoopSubdivisionFilter.h>

int main(int, char *[])
{
	// Create a grid of points (height/terrian map)
	vtkSmartPointer<vtkPoints> points = 
		vtkSmartPointer<vtkPoints>::New();

	unsigned int GridSize = 5;
	double xx, yy, zz;

	points->InsertNextPoint(0, 0, 0);
	points->InsertNextPoint(0, 1, 3);
	points->InsertNextPoint(0, 2, 1);
	points->InsertNextPoint(1, 0, 1);
	points->InsertNextPoint(1, 1, 1);
	points->InsertNextPoint(1, 2, 3);
	points->InsertNextPoint(2, 0, 1);
	points->InsertNextPoint(2, 1, 2);
	points->InsertNextPoint(2, 2, 2);
	points->InsertNextPoint(3, 0, 2);
	points->InsertNextPoint(3, 1, 0);
	points->InsertNextPoint(3, 2, 3);
	

	// Add the grid points to a polydata object
	vtkSmartPointer<vtkPolyData> inputPolyData =
vtkSmartPointer<vtkPolyData>::New();
	inputPolyData->SetPoints(points);

	// Triangulate the grid points
	vtkSmartPointer<vtkDelaunay2D> delaunay =
vtkSmartPointer<vtkDelaunay2D>::New();
#if VTK_MAJOR_VERSION <= 5
	delaunay->SetInput(inputPolyData);
#else
	delaunay->SetInputData(inputPolyData);
#endif
	delaunay->Update();
	vtkPolyData* outputPolyData = delaunay->GetOutput();

	double bounds[6];
	outputPolyData->GetBounds(bounds);

	// Find min and max z
	double minz = bounds[4];
	double maxz = bounds[5];

	// Create the color map
	vtkSmartPointer<vtkLookupTable> colorLookupTable = 
		vtkSmartPointer<vtkLookupTable>::New();
	colorLookupTable->SetTableRange(minz, maxz);
	colorLookupTable->Build();

	// Generate the colors for each point based on the color map
	vtkSmartPointer<vtkUnsignedCharArray> colors =
vtkSmartPointer<vtkUnsignedCharArray>::New();
	colors->SetNumberOfComponents(3);
	colors->SetName("Colors");

	std::cout << "There are " << outputPolyData->GetNumberOfPoints()
		<< " points." << std::endl;

	for(int i = 0; i < outputPolyData->GetNumberOfPoints(); i++)
	{
		double p[3];
		outputPolyData->GetPoint(i,p);

		double dcolor[3];
		colorLookupTable->GetColor(p[2], dcolor);
		unsigned char color[3];
		for(unsigned int j = 0; j < 3; j++)
		{
			color[j] = static_cast<unsigned char>(255.0 * dcolor[j]);
		}

		colors->InsertNextTupleValue(color);
	}

	outputPolyData->GetPointData()->SetScalars(colors);

	vtkSmartPointer<vtkCubeAxesActor> axes =
vtkSmartPointer<vtkCubeAxesActor>::New();
	axes->SetBounds(delaunay->GetOutput()->GetBounds());
	axes->SetFlyModeToOuterEdges();

	axes->XAxisMinorTickVisibilityOff();
	axes->YAxisMinorTickVisibilityOff();
	axes->ZAxisMinorTickVisibilityOff();
	axes->SetXLabelFormat("%6.1f");


 vtkSmartPointer<vtkLoopSubdivisionFilter> subdivide =
vtkSmartPointer<vtkLoopSubdivisionFilter>::New();
  subdivide->SetNumberOfSubdivisions(3);
#if VTK_MAJOR_VERSION <= 5
  subdivide->SetInputConnection(outputPolyData->GetProducerPort());
#else
  subdivide->SetInputData(outputPolyData);
#endif

  // Create a mapper and actor
  vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputConnection(subdivide->GetOutputPort()); 

  	vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
	actor->SetMapper(mapper);

	// Create a renderer, render window, and interactor
	vtkSmartPointer<vtkRenderer> renderer =
vtkSmartPointer<vtkRenderer>::New();
	vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();
	renderWindow->AddRenderer(renderer);
	vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
	renderWindowInteractor->SetRenderWindow(renderWindow);

	//prevents the pointer option from going haywire
	vtkSmartPointer<vtkInteractorStyleTrackballCamera> style =
vtkSmartPointer<vtkInteractorStyleTrackballCamera>::New();
	renderWindowInteractor->SetInteractorStyle(style);

	// Add the actor to the scene
	renderer->AddActor(actor);
	renderer->SetBackground(.1, .2, .3);

	// Render and interact
	renderWindow->Render();

	renderer->GetActiveCamera()->Elevation(290);
	renderer->AddViewProp(axes);
	axes->SetCamera(renderer->GetActiveCamera());

	renderWindowInteractor->Start();

	return EXIT_SUCCESS;
}

Thank you.






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