vtkHardwarePicker and vtkImageData

Support
1

we are trying to use the vtkHardwarePicker to give information about a user hovered location in a data set. With unstructured grids this seems to be working correctly. However with vtkImageData when the user hovers over a cell (cell centered data) I get information from the extracted surface instead of the cell centered data. I am wondering if we are just using this incorrectly or if there are special hoops I need to jump through when using a vtkImageData?

We use a vtkImageToStructuredGrid and vtkDataSetMapper to show the data on screen. Then here is our function to attempt to get information from the vtkHardwarePicker:

std::string GenerateHoverString()
  {
    int* clickPos = m_VisualizationWidget->renderWindow()->GetInteractor()->GetEventPosition();
    vtkNew<vtkHardwarePicker> picker;
    // pick a dataset
    picker->SetSnapToMeshPoint(m_PointPickerOn);
    int const pickResult = picker->Pick(clickPos[0], clickPos[1], 0, m_Renderer);
    if(pickResult == 1)
    {
      vtkDataSet* pickedDataSet = picker->GetDataSet();
      if(pickedDataSet != nullptr)
      {
        vtkIdType cellId = picker->GetCellId();
        vtkIdType pointId = picker->GetPointId();
        if(m_PointPickerOn)
        {
          return printDataValues(pickedDataSet->GetPointData(), pointId, "Point");
        }
        if(m_CellPickerOn)
        {
          return printDataValues(pickedDataSet->GetCellData(), cellId, "Cell");
        }
      }
    }
    return {""};
  }

I am hoping this is just a simple misunderstanding on my part on how to use the vtkHardwarePicker. Maybe I need to work my way back up through the vtk pipeline to find the original source instead of what comes out of the vtkImageToStructuredGrid filter?

2

Why do you use vtkImageToStructuredGrid and not vtkDataSetMapper only?

3

Honestly, not really sure why. It seemed to work for what we needed so we stuck with it. I am not sure of the actual difference. I’m willing to try what ever though.

4

Remove it and see what happens.

5

@Michael_Jackson How are you rendering the image data? Which mapper do you use? If you’re rendering it using the dataset mapper, that just extracts the outer geometry to render - which is why the picker just picks surface cells.