[vtkusers] deleting a face from polydata

[Goodwin Lawlor]

Hi John,

The code you have below wouldn't work because the output of
vtkExtractPolyDataGeometry would have different cell ids to the output
of vtkRemoveCellsFilter.

However, I think you could use vtkSelectVisiblePoints and its
SelectionWindow to brush a surface and get the correct cell ids. I
haven't tried this though. Have a look at the labelledMesh example. It
might be possible to add a SetSource method to save you using RemoveCell
in a loop.

Hth,
Goodwin

-----Original Message-----
From: John Hunter [mailto:jdhunter at nitace.bsd.uchicago.edu] 
Sent: 08 April 2004 15:44
To: goodwin.lawlor at ucd.ie
Cc: vtkusers at vtk.org
Subject: Re: [vtkusers] deleting a face from polydata


>>>>> "Goodwin" == Goodwin Lawlor <goodwin.lawlor at ucd.ie> writes:

    Goodwin> Hi John, vtkPolyData::DeleteCell just marks a cells as a
    Goodwin> VTK_EMPTY_CELL type...  It doesn't actually delete it
    Goodwin> from the dataset.

    Goodwin> I have a class and tcl example that does what you
    Goodwin> want. You can get the source code here:
    Goodwin>
http://www.bioengineering-research.com/vtk/vtkRemoveCellsFilter.htm

Next problem:

For real data, as opposed to the toy sphere examples, the individual
triangle cells that make up my surface are so small and numerous that
I'll be clicking for 2 years before I can get rid of all the ones I
need.  I would like to create a spherical brush to get all the cells
within a region of specified radius from the selected point, and then
remove these cells using your code.  

I am using a vtkExtractPolyDataGeometry filter with a vtkSphere implicit
function.  My question is: can I get the cell ids from the output of
this filter to pass to your code?  

My picker looks like this, with some pseudo-code at the end

def pick_cell(renwinInteractor, event):

    x, y = renwinInteractor.GetEventPosition()

    picker = vtk.vtkCellPicker()
    picker.PickFromListOn()
    picker.AddPickList(actor)
    picker.SetTolerance(0.01)
    picker.Pick(x, y, 0, renderer)

    points = picker.GetPickedPositions()
    numPoints = points.GetNumberOfPoints()
    if numPoints<1: return
    pnt = points.GetPoint(0)
    #mark(*pnt)
    implicit = vtk.vtkSphere()
    implicit.SetCenter(pnt)
    implicit.SetRadius(2)

    extract = vtk.vtkExtractPolyDataGeometry()
    extract.SetImplicitFunction(implicit)
    extract.ExtractInsideOn()
    extract.SetInput(sphere.GetOutput())
    extract.ExtractBoundaryCellsOn()
    extract.Update()

    polyData = extract.GetOutput()

    # here is the pseudo code
    for cellIds in polyData.GetCellIds():
        remove.RemoveCell(cellId)

Is this possible?  Is there a better way to remove the cells inside the
implicit sphere that doesn't require vtkRemoveCellsFilter?

Thanks, 
John Hunter