Cutting structured data Vectorfield

Support
1

Hello everyone,

I am working on displaying a vectorfield. The 3-components vector data is set as point-data in a vtkRectilinearGrid. This is, how I implemented the cutting:

vtkCutter* planeCut = vtkCutter::New();|

planeCut->SetInputData(grid);|
planeCut->SetCutFunction(plane);|
planeCut->SetInputArrayToProcess(0, 0, 0, vtkDataObject::FIELD_ASSOCIATION_POINTS, vtkDataSetAttributes::VECTORS);|
planeCut->Update();|
auto test = planeCut->GetOutput();|

I set the plane origin within the grid coordinates, but what I observe in the output data is that all PointData in vtkDataSet and vtkPolyData have a value of something e +66, which is totally unexpected.

Could someone please confirm if my use of the vtkCutter is correct as it is ?

Kind regards,
Jan

2

Let me share a dummy setup to illustrate my issue:

//Settup grid
	vtkRectilinearGrid* grid = vtkRectilinearGrid::New();
	vtkNew<vtkDoubleArray> xCoo, yCoo, zCoo;
	int numberOfNodesPerDimension = 13;
	int numberOfNodesTotal = std::pow(numberOfNodesPerDimension, 3);
	for (int i = 0; i < numberOfNodesPerDimension; i++)
	{
		xCoo->InsertNextValue(i);
		yCoo->InsertNextValue(i);
		zCoo->InsertNextValue(i);
	}
	grid->SetXCoordinates(xCoo);
	grid->SetXCoordinates(yCoo);
	grid->SetXCoordinates(zCoo);

	vtkNew<vtkDoubleArray> vectorData;
	vectorData->SetNumberOfComponents(3);
	vectorData->SetNumberOfTuples(numberOfNodesTotal);

	for (int i = 0; i < numberOfNodesTotal; i++)
	{
		int value = 13;
		vectorData->SetTuple3(i, value, value, value);
	}
	auto temp = grid->GetPointData()->SetVectors(vectorData);
	grid->GetPointData()->Update();

//Cutting data set
	vtkNew<vtkPlane> plane;
	plane->SetNormal(0, 1, 0);
	plane->SetOrigin(1, 1, 1);

	vtkNew<vtkCutter> cutter;
	cutter->SetInputData(grid);
	cutter->SetCutFunction(plane);
	cutter->SetInputArrayToProcess(0, 0, 0, vtkDataObject::FIELD_ASSOCIATION_POINTS, vtkDataSetAttributes::VECTORS); 
	cutter->Update();
	auto temp = cutter->GetOutput();

	vtkNew<vtkVectorNorm> norm;
	norm->SetInputConnection(cutter->GetOutputPort());
	norm->Update();
	double* range = norm->GetOutput()->GetScalarRange();

The euclidien norm of the inserted vectors is 22.5 but what I get as a range is 0 to 1. I tried to look into the result of the cutter via the temp varaible, but I can’t find any data array in the depth of the vtk output object.

Thus, extending my question from above, I would like to know if there is a possibility to debug the output of the vtkCutter, since I don’t get the expected outcome from the following filter.
Kind regards,
Jan

3

Update:
I solved the issue. Firstly the fixed dummy:

vtkRectilinearGrid* grid = vtkRectilinearGrid::New();
	vtkNew<vtkDoubleArray> xCoo, yCoo, zCoo;
	
	int numberOfNodesPerDimension = 13;
	int numberOfNodesTotal = std::pow(numberOfNodesPerDimension, 3);

	grid->SetDimensions(numberOfNodesPerDimension, numberOfNodesPerDimension, numberOfNodesPerDimension);
	int answ = xCoo->Resize(numberOfNodesPerDimension);
	answ = yCoo->Resize(numberOfNodesPerDimension);
	answ = zCoo->Resize(numberOfNodesPerDimension);
	for (int i = 0; i < numberOfNodesPerDimension; i++)
	{
		xCoo->InsertNextValue(i);
		yCoo->InsertNextValue(i);
		zCoo->InsertNextValue(i);
	}
	grid->SetXCoordinates(xCoo);
	grid->SetYCoordinates(yCoo);
	grid->SetZCoordinates(zCoo);

	vtkNew<vtkDoubleArray> vectorData;
	vectorData->SetNumberOfComponents(3);
	vectorData->SetNumberOfTuples(numberOfNodesTotal);

	for (int i = 0; i < numberOfNodesTotal; i++)
	{
		int value = 13;
		vectorData->SetTuple3(i, value, value, value);
	}
	grid->GetPointData()->SetVectors(vectorData);
	grid->GetPointData()->Update();

	auto temp = grid->GetPointData()->GetVectors();

	//Cutting data set
	vtkNew<vtkPlane> plane;
	plane->SetNormal(0, 1, 0);
    double minOffset = (grid->GetXCoordinates()->GetTuple1(1) - grid->GetXCoordinates()->GetTuple1(0)) / 1000;

	double x = grid->GetXCoordinates()->GetTuple1(0) + minOffset;
	double y = grid->GetYCoordinates()->GetTuple1(0) + minOffset;
	double z = grid->GetZCoordinates()->GetTuple1(0) + minOffset;
	
	plane->SetOrigin(x,y, z);

	vtkCutter* cutter = vtkCutter::New();
	cutter->SetInputData(grid);
	cutter->SetCutFunction(plane);
	cutter->Update();
	auto cutterTemp = cutter->GetOutput()->GetPointData()->GetVectors();

	vtkNew<vtkVectorNorm> norm;
	norm->SetInputConnection(cutter->GetOutputPort());
	norm->NormalizeOff();
	norm->Update();
	double* range = norm->GetOutput()->GetScalarRange();

The observed value with some e +66 is the result when a cut is made outside the data set. It is strange that the vtkCutter cannot perform a cut at the lowest coordinate. This also leads to the strange values mentioned above. On the other hand, the maximum coordinate works fine.
I solved the problem by adding a relative offset to the minimum coordinate.