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

[David Gobbi]

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;
>>>>> }
>>>
>>>
>