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

[Bhanu Hariharan]

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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