[vtkusers] converting vtkImageData to vtkUnstructuredGrid

[David Gobbi]

Use vtkDataSetTriangleFilter to convert your image data (or any
volumetric data) directly into tetrahedrons.  It won't be 2-to-1
ratio, though... it's impossible to generate two tetrahedrons by
cutting a cube in half, so I'm not sure where you got that ratio from.

 - David


On Sun, Apr 10, 2011 at 9:21 AM, Liam Kurmos <quantum.leaf at gmail.com> wrote:
> Does vtk provide a way to turn quads into tetras?
>
> Liam
>
>
> On Sat, Apr 9, 2011 at 11:52 AM, Liam Kurmos <quantum.leaf at gmail.com> wrote:
>> Thanks David!
>>
>> On Sat, Apr 9, 2011 at 11:27 AM, David E DeMarle
>> <dave.demarle at kitware.com> wrote:
>>> It produces voxel cells not tetrahedral cells, so the mapping is one to one.
>>>
>>> David E DeMarle
>>> Kitware, Inc.
>>> R&D Engineer
>>> 28 Corporate Drive
>>> Clifton Park, NY 12065-8662
>>> Phone: 518-371-3971 x109
>>>
>>>
>>>
>>> On Sat, Apr 9, 2011 at 3:59 AM, Liam Kurmos <quantum.leaf at gmail.com> wrote:
>>>> 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
>>>>>>
>>>>>
>>>>
>>>
>>
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