[vtkusers] Not getting to use the vtkThreshold with a vtkRectilinearGrid

[David Doria]

On Fri, Dec 18, 2009 at 12:51 PM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> From vtkThreshold:
> // vtkThreshold is a filter that EXTRACTS CELLS from any dataset type that
> // satisfy a threshold criterion. A cell satisfies the criterion if the
> // scalar value of (every or any) point satisfies the criterion. The
> // criterion can take three forms: 1) greater than a particular value; 2)
> // less than a particular value; or 3) between two values. The output of this
> // filter is an unstructured grid.
>
> I don't think you have defined any cells have you?
>
> On Fri, Dec 18, 2009 at 12:38 PM, David Doria <daviddoria+vtk at gmail.com> wrote:
>> 2009/12/18 Adriano Gonçalves <adriano at esss.com.br>
>>>
>>> Hi David, I've gotten to solve the problem using the method SetInputArrayToProcess thus:
>>>
>>> thresh.SetInputArrayToProcess(0, 0, 0, 1, 'test')
>>>
>>> (this "1" at the 4th parameter is the same of the vtkDataObject::FIELD_ASSOCIATION_CELLS  constant)
>>>
>>> Thank you so much for your help!
>>>
>>> Adriano
>>>
>>
>> Adriano,
>>
>> I'm glad you got it to work, but I'm not sure you used it correctly.
>>
>> In my example:
>> http://www.cmake.org/Wiki/VTK/Examples/Thresholding
>>
>> Since I set the array to the PointData, I used
>>
>> threshold->SetInputArrayToProcess(0, 0, 0,
>> vtkDataObject::FIELD_ASSOCIATION_POINTS,
>> vtkDataSetAttributes::SCALARS);
>>
>> These first three parameters (idx, port, connection) should all be 0
>> because I only have one array and input data set, right? The last two
>> params seem reasonable.
>>
>> Anyone know why this still wouldn't work? Is there no way to set the
>> array to process by it's name as is done with many other filters?
>>
>> Thanks,
>>
>> David

As bill pointed out, vtkThreshold only thresholds cells, even though
you have to specify that you want to threshold cells (very odd).

You can use vtkThresholdPoints to threshold points (this works as expected):
http://www.cmake.org/Wiki/VTK/Examples/Thresholding_Points

I tried to add some triangles and then threshold the values on the
cells, but it is still producing 0 points and cells. I added the array
to the cellData (polydata->GetCellData()->AddArray(index);), changed
one of the parameters to vtkDataObject::FIELD_ASSOCIATION_CELLS, and
changed vtkThresholdPoints to vtkThreshold.
http://www.cmake.org/Wiki/VTK/Examples/Thresholding_Cells

I don't have time to look into this further right now - it's on my
to-do list unless someone gets to it first. Adriano - would you mind
looking into it?

Thanks,

David