Is it possible to implement rubber band picking from a vtkMultiBlockDataSet using vtkExtractGeometry and an ImplicitFunction?

Support
1

Hello!!!

I’ve been experimenting with picking/selection in vtk and started with picking points and cells from a vtkUnstructuredGrid using the frustum from a vtkInteractorStyleRubberBandPick style in a vtkExtractGeometry filter.

When I extend this code to use a vtkMultiBlockDataSet consisting of a hierarchy of vtkUnstructuredGrids as input, the vtkExtractGeometry filter fails to return any cells. The code fragment below works just fine when “target” is a vtkUnstructuredGrid - extract contains the cells inside the frustum. But when mesh is a vtkMultiBlockDataSet, extracted is “None”

        frustum = self.GetInteractor().GetPicker().GetFrustum()

        extract_geometry = vtk.vtkExtractGeometry()
        extract_geometry.SetImplicitFunction(frustum)
        extract_geometry.SetInputData(target)
        extract_geometry.Update()

        extracted = extract_geometry.GetOutput()

Any guidance on how to rubber band pick from a vtkMultiBlockDataSet will be gratefully received.

Doug

2

You can convert multiblock data set to simple polydata using vtkCompositeDataGeometryFilter. I’m not sure if the same works for unstructured grid, too, but if not then there should be a similar filter for that, too.

3

Figured it out…

When using vtkExtractGeometry with a vtkMultiBlockDataSet, the output is not returned via GetOutput, but instead via GetOutputDataObject(0).

    frustum = self.GetInteractor().GetPicker().GetFrustum()

    extract_geometry = vtk.vtkExtractGeometry()
    extract_geometry.SetImplicitFunction(frustum)
    extract_geometry.SetInputData(target)
    extract_geometry.Update()

    extracted = extract_geometry.***GetOutputDataObject(0)***

All(?) of the non composite aware filters return their output this away - in a vtkMultiBlockDataSet. So all downstream operations have to be updated to access vtkMultiBlockDataSets as input.

Works pretty well when you know how!!!

Doug