[vtkusers] converting vtkImageData to vtkUnstructuredGrid

[Liam Kurmos]

I've attempted to convert imagedata to unstructured data as you
suggested some time back using vtkthreshold.
In the code below vtkVol is a vtkImageData with scalar point data.
However when i query the number of cells in the output unstructured
grid i get the same as in the structured data. I would image there
should be twice as many unstructured tetrahedra as cells in the
structured data, can you comment on this?

Liam


    vtkSmartPointer<vtkThreshold>
threshold=vtkSmartPointer<vtkThreshold>::New();
    threshold->SetInput(vtkVol);
    threshold->ThresholdByUpper(0);//scalars are all postive so threshold all
    vtkSmartPointer<vtkUnstructuredGrid> volumeMesh=threshold->GetOutput();
    threshold->Update();
    cout<<" vtkug num cells "<<volumeMesh->GetNumberOfCells()<<endl;
    cout<<" imagedata num cells "<<vtkVol->GetNumberOfCells()<<endl;



On Wed, Feb 9, 2011 at 3:34 PM, David E DeMarle
<dave.demarle at kitware.com> wrote:
> Threshold and many other subsetting filters produce arbitrary sets of
> cells, thus by definition they can not produce structured data.
>
> David E DeMarle
> Kitware, Inc.
> R&D Engineer
> 28 Corporate Drive
> Clifton Park, NY 12065-8662
> Phone: 518-371-3971 x109
>
>
>
> On Wed, Feb 9, 2011 at 10:05 AM, Liam Kurmos <quantum.leaf at gmail.com> wrote:
>> Hi David,
>>
>> Thanks for replying.
>>
>>> One way is to apply the threshold filter and set the threshold so that
>>> it includes the entire scalar range.
>>
>> is it a side affect of the threshold filter that it will also produce
>> an unstructured grid from a structured one?
>>
>> cheers,
>>
>> Liam
>>
>