[vtkusers] Bug in vtkStripper on a very simple case ?

[David Gobbi]

Insert vtkTriangleFilter before vtkStripper.  This will break any
input polylines into line segments.  I don't know if it will help,
but it might.

 - David

On Sun, Dec 9, 2012 at 2:48 PM, pof <jd379252 at gmail.com> wrote:
> yes this is the way LINES objects are written on vtk files.
> Ok, so I understand now the point you were making about the "T", which was
> uncorrect.
>
> So back to the problem, why this vtkStripper is not able to merge those 2
> lines?
>
> Le 09/12/2012 21:41, David Gobbi a écrit :
>>
>> Is it?  Maybe it is.  When you wrote the numbers, I assumed that
>>
>> all of the numbers that you listed were just point indices.
>>
>>
>> On Sun, Dec 9, 2012 at 1:37 PM, pof <jd379252 at gmail.com> wrote:
>>>
>>> Hum I see.
>>> (from what I understand), the first integer of each line is simply the
>>> number of points of the corresponding LINE
>>>
>>> Le 09/12/2012 21:33, David Gobbi a écrit :
>>>
>>>> Then where would the "9" go?
>>>>
>>>> The stripper uses a simple algorithm, it just chooses a starting
>>>> point, goes as far as it can in each direction to create the first
>>>> polyline, and then repeats this procedure until all the line segments
>>>> are accounted for.  It doesn't exhaustively search though all
>>>> permutations to see which one gives the smallest number of output
>>>> polylines... that would cause the algorithm to run many times slower.
>>>>
>>>>
>>>>
>>>>
>>>> On Sun, Dec 9, 2012 at 1:12 PM, pof <jd379252 at gmail.com> wrote:
>>>>>
>>>>> Hi David
>>>>>
>>>>> the first polyline being:
>>>>>
>>>>>     9 0 1 2 3 4 5 19 6 7
>>>>> and the third polyline (actually it is a segment) being:
>>>>>     2 18 0
>>>>> I don't see why they shoud not merge together as (unless I
>>>>> misunderstand
>>>>> something):
>>>>>     10 18 0 1 2 3 4 5 19 6 7
>>>>>
>>>>> Am I wrong?
>>>>>
>>>>>
>>>>> Le 09/12/2012 21:05, David Gobbi a écrit :
>>>>>
>>>>>> Hi JD,
>>>>>>
>>>>>> It could only merge those two lines if it joined them with a "T".
>>>>>> A polyline cannot have any branches.
>>>>>>
>>>>>>     - David
>>>>>>
>>>>>>
>>>>>> On Sun, Dec 9, 2012 at 12:16 PM, pof <jd379252 at gmail.com> wrote:
>>>>>>>
>>>>>>> Hi all,
>>>>>>>
>>>>>>> I get a strange result (which may be a bug) using vtk stripper, i.e.
>>>>>>> it
>>>>>>> does
>>>>>>> not merge LINES as polylines as it is expected to.
>>>>>>> In this example (see below an extract of the polydata produced by
>>>>>>> vtkStripper), only 2 polylines should be obtained, but vtkStripper
>>>>>>> forgot
>>>>>>> to
>>>>>>> merge the first and the third line together, though they obviously
>>>>>>> share
>>>>>>> point with Id=0 (btw, the fact that only Id 0 remains unmerged might
>>>>>>> not
>>>>>>> be
>>>>>>> pure luck).
>>>>>>>
>>>>>>> LINES 3 24
>>>>>>> 9 0 1 2 3 4 5 19 6 7
>>>>>>> 10 9 8 17 13 12 15 14 11 10 16
>>>>>>> 2 18 0
>>>>>>> Does anybody have an idea or an explanation?
>>>>>>> Thanks
>>>>>>> JD
>>>>>>>
>>>>>>> PS: Here below is the complete source file that generates these data
>>>>>>> and
>>>>>>> in
>>>>>>> which vtkStripper is used.
>>>>>>>
>>>>>>> //////////////////////////////////////////////////////
>>>>>>> // Example modified from IntersectionPolyDataFilter.cxx
>>>>>>> //////////////////////////////////////////////////////
>>>>>>> #include <vtkActor.h>
>>>>>>> #include <vtkIntersectionPolyDataFilter.h>
>>>>>>> #include <vtkPolyDataMapper.h>
>>>>>>> #include <vtkPolyDataWriter.h>
>>>>>>> #include <vtkProperty.h>
>>>>>>> #include <vtkRenderer.h>
>>>>>>> #include <vtkRenderWindow.h>
>>>>>>> #include <vtkRenderWindowInteractor.h>
>>>>>>> #include <vtkSmartPointer.h>
>>>>>>> #include <vtkSphereSource.h>
>>>>>>> #include <vtkCellArray.h>
>>>>>>> #include <vtkStripper.h>
>>>>>>>
>>>>>>> int main(int argc, char *argv[])
>>>>>>> {
>>>>>>>      vtkSmartPointer<vtkSphereSource> sphereSource1 =
>>>>>>> vtkSmartPointer<vtkSphereSource>::New();
>>>>>>>      sphereSource1->SetCenter(0.0, 0.0, 0.0);
>>>>>>>      sphereSource1->SetRadius(2.0f);
>>>>>>>      sphereSource1->SetPhiResolution(20);
>>>>>>>      sphereSource1->SetThetaResolution(20);
>>>>>>>      sphereSource1->Update();
>>>>>>>      vtkSmartPointer<vtkPolyDataMapper> sphere1Mapper =
>>>>>>> vtkSmartPointer<vtkPolyDataMapper>::New();
>>>>>>>      sphere1Mapper->SetInputConnection(
>>>>>>> sphereSource1->GetOutputPort()
>>>>>>> );
>>>>>>>      sphere1Mapper->ScalarVisibilityOff();
>>>>>>>      vtkSmartPointer<vtkActor> sphere1Actor =
>>>>>>> vtkSmartPointer<vtkActor>::New();
>>>>>>>      sphere1Actor->SetMapper( sphere1Mapper );
>>>>>>>      sphere1Actor->GetProperty()->SetOpacity(.3);
>>>>>>>      sphere1Actor->GetProperty()->SetColor(1,0,0);
>>>>>>>
>>>>>>>      /////////////////////////
>>>>>>>      // BEGIN MODIFICATIONS //
>>>>>>>      /////////////////////////
>>>>>>>      // Create a planar object
>>>>>>>      // Define 4 vertices
>>>>>>>      vtkSmartPointer<vtkPoints> PlanePoints =
>>>>>>> vtkSmartPointer<vtkPoints>::New();
>>>>>>>      vtkSmartPointer<vtkCellArray> PlaneCells =
>>>>>>> vtkSmartPointer<vtkCellArray>::New();
>>>>>>>      PlanePoints->InsertNextPoint(-3, -1, 0);
>>>>>>>      PlanePoints->InsertNextPoint(3, -1, 0);
>>>>>>>      PlanePoints->InsertNextPoint(-3, 1, 0);
>>>>>>>      PlanePoints->InsertNextPoint(3, 1, 0);
>>>>>>>      // Create 2 trianglar faces
>>>>>>>      PlaneCells->InsertNextCell(3);
>>>>>>>      PlaneCells->InsertCellPoint(0);
>>>>>>>      PlaneCells->InsertCellPoint(1);
>>>>>>>      PlaneCells->InsertCellPoint(2);
>>>>>>>      PlaneCells->InsertNextCell(3);
>>>>>>>      PlaneCells->InsertCellPoint(1);
>>>>>>>      PlaneCells->InsertCellPoint(3);
>>>>>>>      PlaneCells->InsertCellPoint(2);
>>>>>>>      // Create the polydata from points and faces
>>>>>>>      vtkSmartPointer<vtkPolyData> ProtectionWall =
>>>>>>> vtkSmartPointer<vtkPolyData>::New();
>>>>>>>      ProtectionWall->SetPoints(PlanePoints);
>>>>>>>      ProtectionWall->SetPolys(PlaneCells);
>>>>>>>      /////////////////////////
>>>>>>>      // END MODIFICATIONS //
>>>>>>>      /////////////////////////
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkPolyDataMapper> planeMapper =
>>>>>>> vtkSmartPointer<vtkPolyDataMapper>::New();
>>>>>>>      planeMapper->SetInputConnection(
>>>>>>> ProtectionWall->GetProducerPort()
>>>>>>> );
>>>>>>>      planeMapper->ScalarVisibilityOff();
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkActor> planeActor =
>>>>>>> vtkSmartPointer<vtkActor>::New();
>>>>>>>      planeActor->SetMapper( planeMapper );
>>>>>>>      planeActor->GetProperty()->SetOpacity(.3);
>>>>>>>      planeActor->GetProperty()->SetColor(0,1,0);
>>>>>>>
>>>>>>>      // Get intersection segments (LINES) using the
>>>>>>> vtkIntersectionPolyDataFilter
>>>>>>>      vtkSmartPointer<vtkIntersectionPolyDataFilter>
>>>>>>> intersectionPolyDataFilter
>>>>>>> = vtkSmartPointer<vtkIntersectionPolyDataFilter>::New();
>>>>>>>      intersectionPolyDataFilter->SplitFirstOutputOff();
>>>>>>>      intersectionPolyDataFilter->SplitSecondOutputOff();
>>>>>>>      intersectionPolyDataFilter->SetInputConnection( 0,
>>>>>>> sphereSource1->GetOutputPort() );
>>>>>>>      intersectionPolyDataFilter->SetInputConnection( 1,
>>>>>>> ProtectionWall->GetProducerPort() );
>>>>>>>      intersectionPolyDataFilter->Update();
>>>>>>>
>>>>>>>      /////////////////////////
>>>>>>>      // BEGIN MODIFICATIONS //
>>>>>>>      /////////////////////////
>>>>>>>      // Try to get the polylines (there should be 2) from the
>>>>>>> segments
>>>>>>> (LINES)
>>>>>>>      vtkSmartPointer<vtkStripper> stripper =
>>>>>>> vtkSmartPointer<vtkStripper>::New();
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> stripper->SetInputConnection(intersectionPolyDataFilter->GetOutputPort());
>>>>>>>      stripper->Update();
>>>>>>>      // Save resulting polydata on a file, in which we see that there
>>>>>>> are 3
>>>>>>> polylines (actually the second polyline is ok,
>>>>>>>      // but the first and third polylines should have been further
>>>>>>> merged
>>>>>>>      vtkSmartPointer<vtkPolyDataWriter> wr =
>>>>>>> vtkSmartPointer<vtkPolyDataWriter>::New();
>>>>>>>      wr->SetFileName("polylines.txt");
>>>>>>>      wr->SetInputConnection(stripper->GetOutputPort());
>>>>>>>      wr->Write();
>>>>>>>      ///////////////////////
>>>>>>>      // END MODIFICATIONS //
>>>>>>>      ///////////////////////
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkPolyDataMapper> intersectionMapper =
>>>>>>> vtkSmartPointer<vtkPolyDataMapper>::New();
>>>>>>>      intersectionMapper->SetInputConnection(
>>>>>>> stripper->GetOutputPort()
>>>>>>> );
>>>>>>>      intersectionMapper->ScalarVisibilityOff();
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkActor> intersectionActor =
>>>>>>> vtkSmartPointer<vtkActor>::New();
>>>>>>>      intersectionActor->SetMapper( intersectionMapper );
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkRenderer> renderer =
>>>>>>> vtkSmartPointer<vtkRenderer>::New();
>>>>>>>      renderer->AddViewProp(sphere1Actor);
>>>>>>>      renderer->AddViewProp(planeActor);
>>>>>>>      renderer->AddViewProp(intersectionActor);
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkRenderWindow> renderWindow =
>>>>>>> vtkSmartPointer<vtkRenderWindow>::New();
>>>>>>>      renderWindow->AddRenderer( renderer );
>>>>>>>
>>>>>>>      vtkSmartPointer<vtkRenderWindowInteractor> renWinInteractor =
>>>>>>>        vtkSmartPointer<vtkRenderWindowInteractor>::New();
>>>>>>>      renWinInteractor->SetRenderWindow( renderWindow );
>>>>>>>
>>>>>>>      renderWindow->Render();
>>>>>>>      renderWindow->SetSize(600, 600);
>>>>>>>      renderer->SetBackground(0.1, 0.2, 0.4);
>>>>>>>      renWinInteractor->Start();
>>>>>>>
>>>>>>>      return EXIT_SUCCESS;
>>>>>>> }
>>>>>
>>>>>
>