[vtkusers] How to construct polygon?
rakesh patil
prakeshofficial at gmail.com
Mon Apr 17 00:28:08 EDT 2017
Hi,
I thought that vtkTriangleFilter does the tessellation of polygon by
triangulating. Correct me if I am wrong. Let me try your suggestion and
come back.
Thanks
On Mon, Apr 17, 2017 at 7:34 AM, kenichiro yoshimi <rccm.kyoshimi at gmail.com>
wrote:
> Hi,
>
> It looks like the issue of rendering concave polygons by OpenGL included
> in the past mailing list, and it is concluded that OpenGL doesn't render
> concave polygons properly and needs tessellation:
> http://public.kitware.com/pipermail/vtkusers/2010-May/059784.html
> http://vtk.1045678.n5.nabble.com/problems-rendering-
> concave-polygon-td5007789.html
> (I'm sorry I don't know the details of this problem.)
>
> I suggest using vtkDelaunay3D for tessellating and then using
> vtkGeometryFilter that extracts the external faces.
>
> Thanks,
> yoshimi
>
> 2017-04-17 3:30 GMT+09:00 rakesh patil <prakeshofficial at gmail.com>:
>
>> Hi,
>>
>> Well, I would like to know how polygon loop being non-planar leads to
>> such output. Because, the image shown in expectedOutput is also built of
>> similar polygon loop. Its just that for few curved surfaces are rendered
>> properly and few don't. I just want to know why is there such inconsistent
>> behavior and how do I overcome this?
>>
>> Thanks
>>
>> On Sat, Apr 15, 2017 at 10:56 AM, kenichiro yoshimi <
>> rccm.kyoshimi at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> Your polygon loop is non-planar.
>>>
>>>
>>> Howerver, the triangulate method used by vtkPolygon assumes that polygon
>>> points lie in a plane. I recommend to use vtkCylinderSource or
>>> vtkStructuredGrid to represent the side of surface of a cylinder.
>>>
>>> Thanks,
>>> yoshimi
>>>
>>> 2017-04-14 0:38 GMT+09:00 Rakesh Patil <rakesh.p at tataelxsi.co.in>:
>>>
>>>> Hi,
>>>>
>>>>
>>>> This question seems to be simple, but I am not able to get any output
>>>> for this. I am not able to understand what is happening in this case:
>>>>
>>>>
>>>> vtkSmartPointer<vtkPoints> tpoints = vtkSmartPointer<vtkPoints>::New();
>>>>
>>>> vtkSmartPointer<vtkPolygon> poly = vtkSmartPointer<vtkPolygon>::New();
>>>>
>>>> vtkSmartPointer<vtkCellArray> carr = vtkSmartPointer<vtkCellArray>::New();
>>>>
>>>> vtkSmartPointer<vtkPolyData> polyData = vtkSmartPointer<vtkPolyData>::New();
>>>>
>>>>
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 4.39116, -2.39117, 4.5));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 4.39116, -2.39117, 3));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 4.39116, -2.39117, 1.5));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 4.39116, -2.39117, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 4.08748, -2.87967, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 3.05391, -3.95899, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 1.74755, -4.68466, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( 0.28509, -4.99187, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -1.20284, -4.85316, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -2.58332, -4.28094, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -3.73305, -3.32631, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -4.54931, -2.07456, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -4.95919, -0.637487, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -4.92609, 0.856528, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -4.45295, 2.27403, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -3.58205, 3.4884, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -2.39117, 4.39116, 0));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -2.39117, 4.39116, 1.5));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -2.39117, 4.39116, 3));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -2.39117, 4.39116, 4.5));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -2.39117, 4.39116, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -3.58205, 3.4884, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -4.45295, 2.27403, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint( -4.92609, 0.856528, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(-4.95919, -0.637487, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(-4.54931, -2.07456, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(-3.73305, -3.32631, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(-2.58332, -4.28094, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(-1.20284, -4.85316, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(0.28509, -4.99187, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(1.74755, -4.68466, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(3.05391, -3.95899, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(4.08748, -2.87967, 6));
>>>>
>>>> poly->GetPointIds()->InsertNextId(tpoints->InsertNextPoint(4.39116, -2.39117, 6));
>>>>
>>>> carr->InsertNextCell(poly);
>>>>
>>>>
>>>> polyData->SetPoints(tpoints);
>>>>
>>>> polyData->SetPolys(carr);
>>>>
>>>>
>>>> vtkSmartPointer<vtkTriangleFilter> tfilter = vtkSmartPointer<vtkTriangleFilter>::New();
>>>>
>>>> tfilter->SetInputData(polyData);
>>>>
>>>> tfilter->Update();
>>>>
>>>>
>>>>
>>>> vtkSmartPointer<vtkPolyDataMapper> pmapper = vtkSmartPointer<vtkPolyDataMapper>::New();
>>>>
>>>> pmapper->SetInputConnection(tfilter->GetOutputPort());
>>>>
>>>>
>>>> vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
>>>>
>>>> actor->SetMapper(pmapper);
>>>>
>>>> actor->GetProperty()->SetRepresentationToSurface();
>>>>
>>>> actor->GetProperty()->EdgeVisibilityOn();
>>>>
>>>> actor->GetProperty()->SetEdgeColor(1.0, 0.0, 0.0);
>>>>
>>>>
>>>> renderer->AddActor(actor);
>>>>
>>>> renderer->ResetCamera();
>>>>
>>>>
>>>>
>>>> I am not able to view the output if I use vtkTriangleFilter. I have
>>>> attached two screenshots. One is to show how the expected output should
>>>> come. Another is the vtk's output without applying vtkTriangleFilter. How
>>>> do I get the curved surfaces based on the above geometry (points)?
>>>>
>>>>
>>>> Am I missing anything there?
>>>>
>>>>
>>>>
>>>> Thanks & Regards
>>>>
>>>> Rakesh Patil
>>>>
>>>>
>>>>
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>>>
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>>>
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>>
>
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