[vtkusers] Picking field data for unstructured points

[Joseph_Winston at veritasdgc.com]

I have unstructured points, scalars, and field data inside a
vtkPolyData.  A surface is constructed and then displayed by using the
following pipeline:

vtkShepardMethod -> vtkExtractVOI -> vtkGeometryFilter ->
vtkClipPolyData -> vtkWarpScalar -> vtkPolyDataNormals ->
vtkSmoothPolyDataFilter -> vtkCleanPolyData -> vtkTriangleFilter ->
vtkTriangleFilter -> vtkStripper -> vtkDataSetMapper

A vtkPropPicker or a vtkCellPicker is added as an observer on the
vtkCommand::EndPickEvent.

In the callback I can see the field data:

   cout << "number of arrays: " << polyData->GetFieldData()
->GetNumberOfArrays() << endl;
   cout << "first array name: " << polyData->GetFieldData()
->GetArrayName(0) << endl;
   cout << "second array name: " << polyData->GetFieldData()
->GetArrayName(1) << endl;

I then construct a vtkFieldDataToAttributeDataFilter, a
vtkDataObjectToDataSetFilter, and a vtkCellLocator.  I do not see how
I am to get the Cell Connectivity for the vtkDataObjectToDataSetFilter.

   vtkFieldDataToAttributeDataFilter *fd2ad =
vtkFieldDataToAttributeDataFilter::New();
   fd2ad->SetInput(polyData);
   fd2ad->SetInputFieldToDataObjectField();
   fd2ad->SetScalarComponent(0, "Attributes", 0);
   fd2ad->SetOutputAttributeDataToCellData();
   fd2ad->Update();          // Needed???

   vtkDataObjectToDataSetFilter *filter = vtkDataObjectToDataSetFilter::New
();
   filter->SetInput(fd2ad->GetOutput());
   filter->SetCellTypeComponent("Attributes", 0);
//      filter->SetCellConnectivityComponent("???", X);  // how is this
done?
   filter->Update();          // Needed???

   vtkCellLocator *locator = vtkCellLocator::New();
   locator->SetDataSet(filter->GetOutput());

   // ******
   // The "problem" occurs here in BuildLocator since it returns
   // because (numCells = this->DataSet->GetNumberOfCells()) < 1 )
   // ******
   locator->BuildLocator();

   float closestPoint[3];
   vtkIdType cellId = 0;
   int subId = 0;
   float dist2 = 0;

   // ******
   // This call fails since this->NumberOfOctants is not set.
   // ******

   locator->FindClosestPoint(pickPos,
                             closestPoint,
                             cellId,
                             subId,
                             dist2);

Where do I get the Cell Connectivity in my pipeline since I'm starting
with unstructured data?  Or what should I do to pick field data when
I'm starting with unstructured points?

Thanks





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