[vtkusers] How to extract area of (triangle) Cells?

[David E DeMarle]

I suppose the reason it is not there in the first place is the design
goal of not adding overhead. That class is pretty deep down in VTK.
Adding a method to the class grows the class's function lookup table
which makes vtkTriangle's infinitesimally slower to use. Since there
are usually many Triangles, and they are used in many places that
infinitesimal overhead can add up. Thus, adding that convenience
method then was left to user's application which can do it externally
to the class.

That said I still don't have a problem with adding it. Others can say
no if they think the added overhead is not worth the added
convenience.

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109

On Fri, Dec 18, 2009 at 11:01 AM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
> David,
>
> I looked at the source for vtkMeshQuality and I think you have
> uncovered a bug. I see vtkDoubleArray named "Quality" added to the
> cell data, but I do not see where any data is added to the array.
>
> I noticed that that Graphics/Texting/Cxx/MeshQuality does not access
> the CellData.
>
> If it's not tested it's broken,
>
> Bill
>
> On Fri, Dec 18, 2009 at 8:10 AM, David Doria <daviddoria+vtk at gmail.com> wrote:
>> On Thu, Dec 17, 2009 at 11:14 AM, Bryn Lloyd <blloyd at vision.ee.ethz.ch>
>> wrote:
>>>
>>> David,
>>>
>>> Not sure, but it works in paraview doesn't it?
>>>
>>> 1. Maybe inverted triangles (there was an issue in the past with inverted
>>> tets).
>>>
>>> 2. Maybe you don't have triangles, but strips?
>>>
>>> /Bryn
>>>
>>
>> Bryn,
>> Hmm, I tried it with a sphere source run through vtkTriangleFilter. This
>> should produce good triangles, right?
>>   vtkSmartPointer<vtkSphereSource> sphereSource =
>> vtkSmartPointer<vtkSphereSource>::New();
>>   sphereSource->Update();
>>
>>   vtkSmartPointer<vtkTriangleFilter> triangleFilter =
>> vtkSmartPointer<vtkTriangleFilter>::New();
>>   triangleFilter->SetInputConnection(sphereSource->GetOutputPort());
>>   triangleFilter->Update();
>>
>>   //vtkPolyData* mesh = sphereSource->GetOutput();
>>   vtkPolyData* mesh = triangleFilter->GetOutput();
>>   cout << "There are " << mesh->GetNumberOfCells() << " cells." << endl;
>>
>>   vtkSmartPointer<vtkMeshQuality> qualityFilter =
>> vtkSmartPointer<vtkMeshQuality>::New();
>>   qualityFilter->SetInput(mesh);
>>   qualityFilter->SetTriangleQualityMeasureToArea();
>>   qualityFilter->Update();
>>
>>   vtkDataSet* qualityMesh = qualityFilter->GetOutput();
>>   vtkSmartPointer<vtkDoubleArray> qualityArray =
>> vtkDoubleArray::SafeDownCast(qualityMesh->GetCellData()->GetArray("Quality"));
>>
>>   cout << "There are " << qualityArray->GetNumberOfTuples() << " values." <<
>> endl;
>>
>>   for(unsigned int i = 0; i < qualityArray->GetNumberOfTuples(); i++)
>>     {
>>     double val;
>>     qualityArray->GetValue(i);
>>     cout << "value " << i << " : " << val << endl;
>>     }
>> The output is still
>> ...
>> value 90 : 5.77804e-269
>> value 91 : 5.77804e-269
>> value 92 : 5.77804e-269
>> ...
>> Any thoughts?
>> Thanks,
>>
>> David
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