[vtkusers] VTK C++ : How to perform a velocity interpolation computation from a vtkMultiBlockDataSet with celldata?

[Biddiscombe, John A.]

The interpolated velocity field classes are not written as filters. They are for internal use within other specialized classes like the stream/pathline filters.

Can you explain what you want to achieve at a more filter-like level?

JB

From: vtkusers-bounces at vtk.org [mailto:vtkusers-bounces at vtk.org] On Behalf Of Guillaume Jacquenot
Sent: 19 January 2012 12:32
To: vtkusers at vtk.org
Subject: [vtkusers] VTK C++ : How to perform a velocity interpolation computation from a vtkMultiBlockDataSet with celldata?

Dear all,

My objective is to retrieve a velocity vector from an interpolation computation from a vtkMultiBlockDataSet with vtkUnstructuredGrid containing velocity vectors.
My velocity vectors are located at the center of cells, not the points.
I managed to retrieve the velocity vector from a cell with vtkCellLocator.
However I want more accurate results, and thus perform data interpolation, depending on the requested point.

For this, I want to use the class vtkInterpolatedVelocityField or vtkCellLocatorInterpolatedVelocityField
To do so, I see that i have to create an instance of vtkInterpolatedVelocityField or vtkCellLocatorInterpolatedVelocityField and use the method addDataSet to feed this instance.
I have tried to do so with dataSet contained in my vtkMultiBlockDataSet. However, the method FunctionValues always returned "Can't evaluate dataset". I figured out that message was sent because my data are located at cell-centered not point-centered.
Therefore I want to convert my cell-centered data to point-centered data.
I know that I have to use the class vtkCellDataToPointData, but I don't manage to retrieve the result and send it as input to an instance of vtkInterpolatedVelocityField or vtkCellLocatorInterpolatedVelocityField.
vtkCellDataToPointData is a sub-class of vtkAlgorithm, and I have seen it is nice to work with inputport, outputport methods.
However, class vtkInterpolatedVelocityField is a sub-class of vtkFiltering, and does not have such connexion methods.

The general question is how to pass result from an instance of vtkCellDataToPointData to an instance of vtkInterpolatedVelocityField

I have tried unsuccessfully the method GetOutputDataObject and GetUnstructuredGridOutput on a instance of vtkCellDataToPointData . Cause the program to crash.
dataObj = c2p->GetOutputDataObject(0);
unstructuredGrid = c2p->GetUnstructuredGridOutput();

More precisely, my questions are the followings:
- Can I add "inplace" point data to a vtkMultiBlockDataSet from the cell data? That means that I add point data to my vtkMultiBlockDataSet containing cell data, with algorithm vtkCellDataToPointData. If possible, I guess I can use the method addDataset from vtkInterpolatedVelocityField.
- Can I work directy on a vtkMultiBlockDataSet with vtkCellDataToPointData on my function presented below, ie use c2p->SetInput(vtkMultiBlockDataSet) where c2p is a vtkCellDataToPointData?


Below is the function I want to develop with VTK 5.8. It compiles, but crashes at run time.
The vtkOuputWindow reports a problem with vtkExecutive at line 756.cxx  vtkStreamingDemandDrivenPipeline : Algorithm vtkCellDataToPointData ...
However on Windows, I cant read all the error message, and report it here.
For time being, the function does not return anything. I don't know for time being, if it will return a modified version of multiBlockDataSet, with cell data, or if it will return an instance of vtkInterpolatedVelocityField

void convertCellDataToPointData(vtkSmartPointer<vtkMultiBlockDataSet> & multiBlockDataSet)
{
    vtkSmartPointer<vtkCellDataToPointData> c2p = vtkSmartPointer<vtkCellDataToPointData>::New();
    c2p->DebugOn();
    c2p->SetInput(multiBlockDataSet);
    c2p->PassCellDataOff();
    c2p->Update();
    std::cout<<"c2p->Print(std::cout)"<<std::endl;
    c2p->Print(std::cout);
    c2p->UpdateInformation();
    c2p->UpdateWholeExtent();
    std::cout << "c2p->GetTotalNumberOfInputConnections = " << c2p->GetTotalNumberOfInputConnections()<<std::endl;
    std::cout << "c2p->GetNumberOfInputPorts            = " << c2p->GetNumberOfInputPorts()<<std::endl;
    std::cout << "c2p->GetNumberOfOutputPorts           = " << c2p->GetNumberOfOutputPorts()<<std::endl;

    vtkSmartPointer<vtkDataObject> dataObj = vtkSmartPointer<vtkDataObject>::New();
    std::cout <<"H1"<<std::endl;
    dataObj = c2p->GetOutputDataObject(0);
    std::cout <<"H2"<<std::endl;
    dataObj->Print(std::cout); // Crash vtkStreamingDemandDrivenPipeline : Algorithm vtkCellDataToPointData ...

    vtkSmartPointer<vtkUnstructuredGrid> unstructuredGrid = vtkSmartPointer<vtkUnstructuredGrid>::New();
    unstructuredGrid = c2p->GetUnstructuredGridOutput();
    std::cout <<"H3"<<std::endl;
    std::cout<<"unstructuredGrid->GetNumberOfCells   = "<<unstructuredGrid->GetNumberOfCells()<<std::endl; // Crash vtkStreamingDemandDrivenPipeline : Algorithm vtkCellDataToPointData ...
    std::cout<<"unstructuredGrid->GetNumberOfPoints  = "<<unstructuredGrid->GetNumberOfPoints()<<std::endl;
    std::cout <<"H4"<<std::endl;
    unstructuredGrid->Print(std::cout);
    std::cout <<"H5"<<std::endl;
}

I work with version 5.8 of VTK. I use Win32.

Thanks for considering my problem.
Maybe an example can be generated on the VTK wiki from my problem.

Guillaume Jacquenot
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