[vtkusers] vtkProbeFilter inconsistency

[Sujin Philip]

Hi Santosh,


> If I understand correctly, the method you suggested will give the value of
> the scalar from the cell data.
>
Correct.

However, I want to get the interpolated value at any arbitrary position,
> which is why I felt the probe filter is the correct choice(?).
>
Probe filter will do that for you. If it is just a few points you can also
use the "weights" you get from the call to "FindCell" to do the
interpolation yourself. There is an overloaded "FindCell" that will give
you the "vtkCell". From there, you can get the ids of the cell's points.


> Of what I understand, the probe filter returns interpolated point data or
> it returns the cell data if the point data is not available.
>
Your understanding is correct.


> On my data set, the probe filter's output has all the arrays of the point
> data but the values are all zero. This happens on probing random positions
> on the surface of the dataset. Do let me know if you need any further
> information.
>
If the cells in your input dataset are 2D cells then the tolerance maybe
the issue. Try setting ComputeTolerence to false and experiment with
SetTolerance and see if that works.

Thanks
Sujin


On Thu, Aug 16, 2018 at 8:53 AM, Santosh Biradar <scbiradar at gmail.com>
wrote:

> Thanks a lot Sujin.
> If I understand correctly, the method you suggested will give the value of
> the scalar from the cell data.
> I am assuming I can use FindPoint to get the closest point and get the
> point data from that point id.
> However, I want to get the interpolated value at any arbitrary position,
> which is why I felt the probe filter is the correct choice(?).
> Of what I understand, the probe filter returns interpolated point data or
> it returns the cell data if the point data is not available.
> On my data set, the probe filter's output has all the arrays of the point
> data but the values are all zero. This happens on probing random positions
> on the surface of the dataset. Do let me know if you need any further
> information.
>
> Thanks again,
> Santosh
>
>
>
> On Tue, Aug 14, 2018 at 7:39 PM, Sujin Philip <sujin.philip at kitware.com>
> wrote:
>
>> Hi Santosh,
>>
>> I cannot say for sure what is going wrong in the probe filter without
>> more information. Looking at your code it looks like all you want to do is
>> to find a cell that contains a given point and get its cell attribute. An
>> easier way to achieve that would be:
>>
>> tol2 = 1e-6;
>> double pcoords[3];
>> double weights[8]; // size based on the max number of points in any of
>> "input's" cells
>> double pt[3] = { x, y, z };
>> auto cellId = input->FindCell(pt, NULL, -1, tol2, 0, pcoords, weights);
>> auto attr = vtkDataArray::SafeDownCast(input->GetCellData().GetAbstractA
>> rray("T"));
>> double val = 0.0;
>> attr->GetTuple(cellId, &val);
>>
>> Hope this helps
>>
>> -Sujin
>>
>>
>> On Tue, Aug 14, 2018 at 7:54 AM, Santosh Biradar <scbiradar at gmail.com>
>> wrote:
>>
>>> Hi VTKers,
>>>
>>> I am trying to use the vtkProbeFilter on an unstructured data set. I am
>>> using a cell to point filter on my input dataset and trying to probe the
>>> output of the cell to point filter
>>>
>>> I have a snippet for what I am doing:
>>>
>>> #picker for getting the point
>>> picker = vtk.vtkCellPicker()
>>> picker.PickFromListOn()
>>> picker.AddPickList(c2pactor)
>>> picker.SetTolerance(0.000001*reader.GetOutput().GetLength())
>>> picker.Pick(x, y, 0, renderer)
>>> points = picker.GetPickedPositions()
>>> numPoints = points.GetNumberOfPoints()
>>> print numPoints
>>> if numPoints < 1:
>>>     return
>>> pnt = points.GetPoint(0)
>>>
>>> #probe filter
>>> pt = vtk.vtkPoints()
>>> pt.InsertPoint(0, x, y, z)
>>> polydata = vtk.vtkPolyData()
>>> polydata.SetPoints(pt)
>>> probe = vtk.vtkProbeFilter()
>>> probe.SetInputData(polydata)
>>> probe.SetSourceData(c2p.GetOutput())
>>>
>>> probe.Update()
>>>
>>> val = probe.GetPolyDataOutput().GetPointData().GetScalars("T").Get
>>> Range(0)[0]
>>>
>>> Now, I am getting inconsistent behavior of the probe filter.
>>> Sometimes, I get the values of all the point data arrays as 0.0 for the
>>> probed location.
>>> I dont understand this behavior. It does work correctly but not always.
>>>
>>>
>>> Alternately, I tried using the picker.GetCellId() and
>>> picker.GetPointId() to directly fetch the value from the actor's input
>>> dataset (in this case, output of cell to point filter). Again here, the
>>> point id obtained always seems to be only a particular point in the cell
>>> irresepctive of whether probed location is near that point or any other
>>> point in that cell. So, I end up getting point data of a particular point
>>> in that cell no matter where I probe in that cell.
>>> Is using a vtkPointPicker the correct option here?
>>>
>>> Also, should I explore using vtkPointLocator/vtkCellLocator ?
>>>
>>> I hope the question is clear. I am using VTK-6.3 on Windows.
>>>
>>> Thanks,
>>> Santosh
>>>
>>>
>>>
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>>
>
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