[vtkusers] triangle - triangle intersection VTK C++

[nolvis]

I am bit confused how Triangle - triangle intersection works in VTK. When im
using points commented as Shares an edge z = 0 it shows that intersection
doesn't exist, but when im using points commented as Shares an edge z = 5 ,
i am getting intersection. Why is that?

//VTK includes
#include <vtkSmartPointer.h>
#include <vtkCellArray.h>
#include <vtkTriangle.h>
#include <vtkLine.h>
//render
#include <vtkActor.h>
#include <vtkRenderer.h>
#include <vtkRenderWindow.h>
#include <vtkRenderWindowInteractor.h>
#include <vtkProperty.h>
//polydata
#include <vtkPolyData.h>
#include <vtkPolyDataMapper.h>
#include <vtkIntersectionPolyDataFilter.h>

//default includes
#include <iostream>
using namespace std;

void displayPoly(vtkSmartPointer<vtkPolyData> &polyData);

int main(int , char *[])
{
  // Creates a polydata object
  vtkSmartPointer<vtkPolyData> polyData =
vtkSmartPointer<vtkPolyData>::New();

  // creates a point object
  vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
  //Shares an edge z = 5
  points->InsertNextPoint ( 0.0, 0.0, 0.0 );
  points->InsertNextPoint ( 5.0, 0.0, 0.0 );
  points->InsertNextPoint ( 0.0, 5.0, 0.0 );
  points->InsertNextPoint ( 0.0, 5.0, 0.0 );
  points->InsertNextPoint ( 5.0, 0.0, 0.0 );
  points->InsertNextPoint ( 10.0, 10.0, 5.0 );

  //Shares an edge z = 0
  // points->InsertNextPoint ( 0.0, 0.0, 0.0 );
  // points->InsertNextPoint ( 5.0, 0.0, 0.0 );
  // points->InsertNextPoint ( 0.0, 5.0, 0.0 );
  // points->InsertNextPoint ( 0.0, 5.0, 0.0 );
  // points->InsertNextPoint ( 5.0, 0.0, 0.0 );
  // points->InsertNextPoint ( 10.0, 10.0, 0.0 );

  vtkSmartPointer<vtkCellArray> triangles =
vtkSmartPointer<vtkCellArray>::New();
  for(int i = 0; i < 2; i++){
    vtkSmartPointer<vtkTriangle> triangle =
vtkSmartPointer<vtkTriangle>::New();
    triangle->GetPointIds()->SetId ( 0, i*3 );
    triangle->GetPointIds()->SetId ( 1, i*3+1 );
    triangle->GetPointIds()->SetId ( 2, i*3 + 2 );

    //add the triangles to the list of triangles
    triangles->InsertNextCell ( triangle );
  }

  polyData->SetPoints ( points );
  polyData->SetPolys ( triangles );
  vtkSmartPointer<vtkCellArray> cells =
vtkSmartPointer<vtkCellArray>::New();
  cells = polyData->GetPolys();
  cells->InitTraversal();
  vtkSmartPointer<vtkIdList> idList = vtkSmartPointer<vtkIdList>::New();
  vtkSmartPointer<vtkIntersectionPolyDataFilter> filter =
vtkSmartPointer<vtkIntersectionPolyDataFilter>::New();

  while(cells->GetNextCell(idList))
  {
    vtkIdType i = cells->GetTraversalLocation();
    double a[3], b[3], c[3];
    polyData->GetPoint(idList->GetId(0), a);
    polyData->GetPoint(idList->GetId(1), b);
    polyData->GetPoint(idList->GetId(2), c);

    while(cells->GetNextCell(idList)){
      double e[3], f[3], g[3], pt1[3], pt2[3], surfaceid[2], tolerance;
      polyData->GetPoint(idList->GetId(0), e);
      polyData->GetPoint(idList->GetId(1), f);
      polyData->GetPoint(idList->GetId(2), g);

      int coplanar;
      int intersect = filter->TriangleTriangleIntersection(a, b, c, e, f, g,
coplanar, pt1, pt2, surfaceid, tolerance);
      if(intersect == 1){
        cout << "triangle to compare with" << endl;
        cout << a[0] << " " << a[1] << " " << a[2] << endl;
        cout << b[0] << " " << b[1] << " " << b[2] << endl;
        cout << c[0] << " " << c[1] << " " << c[2] << endl;

        cout << "comperable  triangle" << endl;
        cout << e[0] << " " << e[1] << " " << e[2] << endl;
        cout << f[0] << " " << f[1] << " " << f[2] << endl;
        cout << g[0] << " " << g[1] << " " << g[2] << endl;
        cout << "Intersection of triangles" << endl << endl;
        cout << "coplanar: " << coplanar << endl;
        cout << "pt1: " << pt1[0] << " " << pt1[1] << " " << pt1[2] << endl;
        cout << "pt2: " << pt2[0] << " " << pt2[1] << " " << pt2[2] << endl;
        cout << "surfid: " << surfaceid[0] << " " << surfaceid[1] << endl;
        cout << "tolerance: " << tolerance << endl;
        cout << "Intersect: " << intersect << endl;
      }
    }
    cells->SetTraversalLocation(i);
    }
  displayPoly(polyData);
}

void displayPoly(vtkSmartPointer<vtkPolyData> &polyData){
  //mapper
  vtkSmartPointer<vtkPolyDataMapper> mapper =
vtkSmartPointer<vtkPolyDataMapper>::New();
  mapper->SetInputDataObject(polyData);

  //actor
  vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
  actor->SetMapper(mapper);
  actor->GetProperty()->SetRepresentationToWireframe();

  //render
  vtkSmartPointer<vtkRenderer> renderer =
vtkSmartPointer<vtkRenderer>::New();
  vtkSmartPointer<vtkRenderWindow> renderWindow =
vtkSmartPointer<vtkRenderWindow>::New();
  renderWindow->AddRenderer(renderer);

  //renderWindow
  vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
vtkSmartPointer<vtkRenderWindowInteractor>::New();
  renderWindowInteractor->SetRenderWindow(renderWindow);
  renderer->AddActor(actor);
  renderWindow->Render();
  renderWindowInteractor->Start();
}





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