[vtkusers] vtkSelection with GLOBALIDS, vtkExtractSelection returns empty

[da xu]

Hey all,

I am trying to extract a section of my datasets using vtkSelection. I
currently have a GUI that the user clicks on to select a start and end point
using vtkPointPicker, returning the PointID. With a starting POINTID and
ending POINTID, i then use a vtkSelection with field type POINT, ContentType
GLOBALIDS to extract a dataset containing the points (with
vtkSelectionNode's SetSelectionList correctly set I believe). However, I
always end up extracting an empty grid.

I can't figure out if:
 My vtkSelectionNode is set up incorrectly
 I'm using vtkExtractSelection incorrectly.
 The vtkPointPicker doesnt actually get GLOBALIDS ?
 Missing an update somewhere?

Here is the code:

// Set up vtkSelectionNode
    vtkSelection* selection = vtkSelection::New();
    vtkSelectionNode* selectionNode = vtkSelectionNode::New();
    selectionNode->SetFieldType(vtkSelectionNode::POINT);
    selectionNode->SetContentType(vtkSelectionNode::GLOBALIDS);

// Populate the selection node with our GLOBALIDS (obtained from
vtkPointPicker)
    vtkIntArray* intarray = vtkIntArray::New();
    for (int a = first; a < second; a++)
    {
        intarray->InsertNextValue(a);
    }
    selectionNode->SetSelectionList(intarray);
    selection->AddNode(selectionNode);

// Some setup stuff, Our source data is from a multiblock data set
    vtkMultiBlockDataSet *extractFrom = vtkMultiBlockDataSet::SafeDownCast(
m_v_modules.at(0)->getDataObject());
    int nblocks = extractFrom->GetNumberOfBlocks();

    vtkGeometryFilter *filter = vtkGeometryFilter::New();
    vtkDataSetMapper *mapper = vtkDataSetMapper::New();
    int counter=0;
    vtkExtractSelection* extractSelection = vtkExtractSelection::New();

// Iterate through our datasets (structured grids) and apply
vtkExtractSelection to them. Always extracts empty!
    vtkCompositeDataIterator *iter = extractFrom->NewIterator();
    iter->InitTraversal();

    int totalpoints = 0;
    while (!iter->IsDoneWithTraversal())
    {
        vtkDataSet* ds =
vtkDataSet::SafeDownCast(iter->GetCurrentDataObject());
        if (ds)
        {
            const char* name = ds->GetClassName();    /// Temp debugger
            extractSelection->RemoveAllInputs();
            extractSelection->SetInput(0, ds);    /// Set the vtkDataSet for
extraction
            extractSelection->SetInput(1, selection);    /// Set the
vtkSelection for extraction
            vtkDataObject* extracted = extractSelection->GetOutput();
            extractSelection->Update();
            const char* name2 = extracted->GetClassName();    /// Temp
debugger

            vtkUnstructuredGrid* unstructGridTest =
vtkUnstructuredGrid::SafeDownCast(extracted);
            int ntemp1 = unstructGridTest->GetNumberOfPoints();
            totalpoints += ntemp1;
            counter++;
        }
        iter->GoToNextItem();
    }
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