[vtk-developers] [vtkusers] vtkDataSetSurfaceFilter - Cell Picking

[David E DeMarle]

Give DSF a name for the array.
SetOriginalCellIdsName("idsintoDSForsomething")
Then retrieve it from the output like
DSF->GetOutput()->GetCellData()->GetArray("idsintoDSForsomething")


David E DeMarle
Kitware, Inc.
R&D Engineer
21 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-881-4909


On Wed, Mar 6, 2013 at 11:29 AM, Bhanu Hariharan <bhanu at petrotel.com> wrote:

>
> David,
>
> I had turned on PassThroughCell. But I do not know how to access the new
> Ids array after the fact.
> VTK Doc says something about a 'OrginalCellIds' but I am not sure how to
> access this.
> So I extracted the output of DSF to a vtkPolyData but still cant figure
> out how to get to that new Ids array.
> Any help with that is really appreciated.
>
> I will try your other suggestion in the meantime.
>
> Thanks,
> Bhanu
>
>
> On Wed, Mar 6, 2013 at 9:25 AM, David E DeMarle <dave.demarle at kitware.com>wrote:
>
>> Sorry for the confusion, it has been a long time since I added that code
>> the DataSetSurfaceFilter. Turning PassThroughCell/PointIds in fact
>> generates a new Ids array, which you can retrieve after the fact to do the
>> lookups into the data that is input to the DSF and extract particular
>> cells/points by their offset (n'th cell in the cell array, n'th point in
>> the point array)
>>
>> However I still recommend making your own ids array and using that
>> instead of PassThrough. vtkIdFilter will generate them for you. The array
>> marked as the active global ids array is treated specially by most filters
>> in that they try to preserve it across operations (including threshold and
>> DSF). We added this to VTK a few years ago specifically for this case of
>> finding out where particular result values come from (and in particular for
>> surface selection). So the Threshold and surface filter will push globalIDS
>> forward just fine. Once you get a result, grab the active globaIDs array,
>> look for the values in it, and look them up in the original data. The
>> extract selections filter will do the job of looking them up in the
>> original data and pulling them out as a new dataset.
>>
>>
>> David E DeMarle
>> Kitware, Inc.
>> R&D Engineer
>> 21 Corporate Drive
>> Clifton Park, NY 12065-8662
>> Phone: 518-881-4909
>>
>>
>> On Wed, Mar 6, 2013 at 10:02 AM, Bhanu Hariharan <bhanu at petrotel.com>wrote:
>>
>>> David,
>>> Thanks for replying. However I have a doubt.
>>> Are you suggesting the VTKUnstructuredgrid should have an globalids
>>> array? Is that what the member is called - globalIds? I actually pass
>>> VTKUnstructuredgrid  to a VTKThreshold filter and then pass that filter to
>>> VTKdatasetsurfacefilter.
>>>
>>> Perhaps you can post a couple lines of code. That would be very helpful.
>>> Thanks,
>>> Bhanu
>>>
>>>
>>>
>>> On Tue, Mar 5, 2013 at 6:55 PM, David E DeMarle <
>>> dave.demarle at kitware.com> wrote:
>>>
>>>> The input data should have a globalids array containing a unique value
>>>> for each cell. If it does, extract will preserve it. After the extraction,
>>>> use that array in the polydata to do the look up to the original cell in
>>>> the unstructured grid.
>>>> On Mar 5, 2013 6:00 PM, "Bhanu Hariharan" <bhanu at petrotel.com> wrote:
>>>>
>>>>> Hi All,
>>>>>
>>>>> I need some help doing the following. Please could one of you guide me
>>>>> on how.
>>>>>
>>>>> I use a vtkDataSetSurfaceFilter on VTKUnstructuredGrid to render skin
>>>>> of that grid. That works fine and I can see the number of surfaces shown by
>>>>> grabbing the
>>>>> dataSetSurfaceFilter->GetOutput()->GetNumberOfCells().
>>>>>
>>>>>
>>>>> I need a way to map the surface back to the original cell id. That is
>>>>> if I have 2 cells and I render just skin, number of surfaces rendered are
>>>>> 10. I need to be able to pick on any of these 10 surfaces and map them back
>>>>> to either of the the 2 grid cells.
>>>>>
>>>>>
>>>>> http://www.vtk.org/doc says :
>>>>>
>>>>> If PassThroughCellIdsOn is 1, then the output polygonal dataset will
>>>>> have a celldata array that holds the cell index of the original 3D cell
>>>>> that produced each output cell. This is useful for cell picking.
>>>>> I turned the PassThroughCellIds On and I have UseStrips turned off.
>>>>>
>>>>> Then I did
>>>>> vtkPolyData *surfacePolyData = dataSetSurfaceFilter->GetOutput();
>>>>>
>>>>> But I do not see how I can access that celldata array that holds the
>>>>> original 3D cells for the surfaces.
>>>>>
>>>>> Please can anyone advise on how.
>>>>>
>>>>> Thanks in advance.
>>>>> Bhanu
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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>
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