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

[David E DeMarle]

The virtual method lookup overhead is what I was thinking about. Sorry
for not explicitly stating that.

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 11:48 AM, David Gobbi <david.gobbi at gmail.com> wrote:
> What overhead is there, as long as it isn't declared as a virtual method?
>
> I think the addition is fine, myself.  My only objection would be the
> usual: instantiating a vtk object to do a computation is inefficient.
> It's probably too late to add lightweight stack-based math objects to
> VTK, so in general, people should use the static methods even if it
> does mean that they have to write a few more lines of code.  But for
> the sake of the wrappers, these sort of convenience methods can be
> useful.
>
>   David
>
>
> On Fri, Dec 18, 2009 at 9:29 AM, David E DeMarle
> <dave.demarle at kitware.com> wrote:
>> 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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