Delete the overlapping of the same Polygon(polydata)

Support
1

image

Hi there, I push some points in vtkPoints and generate vtkCellArray to get a track of mouse with vtkActor2D and vtkPolydataMapper2D to clip the body. Before I execute clipping volume, I found that the overlapping of polygon is showed like the picture above.

What I want is like this, to detect the overlapping points and unregister them
image
(the original site is How to only render one vtkRender in vtkRenderWindow with two vtkRenders - Development - VTK)

Could you give me some advice to deal with the polydata? I tried to use vtkCleanPolydata to update but make no sense.

Here is some of my code:

	m_pTitleRenderer->SetLayer(1);

	m_pBMRenderer->SetDisplayPoint(fx, fy, 0);
	double worldcoortemp[4];
	m_pBMRenderer->DisplayToWorld();
	m_pBMRenderer->GetWorldPoint(worldcoortemp);

	wVector2<float> temp;
	temp.x = fx;
	temp.y = fy;
	m_fSaveClipPoints.push_back(temp);

	m_pPoints = vtkSmartPointer<vtkPoints>::New();
	for (int i = 0; i < m_fSaveClipPoints.size(); i++) {
		m_pPoints->InsertNextPoint(m_fSaveClipPoints[i].x, m_fSaveClipPoints[i].y, 0.0);
	}

	int pointnum = m_pPoints->GetNumberOfPoints();

	m_pDisplayPlane = vtkSmartPointer<vtkCellArray>::New();
	m_pDisplayPlane->InsertNextCell(m_pPoints->GetNumberOfPoints() + 1);
	for (int i = 0; i < m_fSaveClipPoints.size(); i++) {
		m_pDisplayPlane->InsertCellPoint(i);
	}
	m_pDisplayPlane->InsertCellPoint(0); // start points

	int cellnum = m_pDisplayPlane->GetNumberOfCells();

	// polydata
	m_pPolygonTrack->SetPoints(m_pPoints);
	m_pPolygonTrack->SetPolys(m_pDisplayPlane);

        ////// It seems some processing here to deal with the polygon

	// polyline property setting
	vtkNew<vtkProperty2D> _ptpro;
	_ptpro->SetLineWidth(5);
	_ptpro->SetColor(1.0, 1.0, 0);
	_ptpro->SetOpacity(0.4);
	_ptpro->SetPointSize(5);

	m_pDisplayActor->SetProperty(_ptpro);

	m_pDisplayMapper->SetInputData(m_pPolygonTrack);
	m_pDisplayActor->SetMapper(m_pDisplayMapper);
	m_pTitleRenderer->AddActor(m_pDisplayActor);

	m_pRenderWnd->Render();

	m_nPointCount++;

Thanks for any advice!!!

2

@dgobbi
Hi, Mr!
I notice that you had given some useful advice in the post(How to only render one vtkRender in vtkRenderWindow with two vtkRenders - #8 by Pisces2018) Could you please give me some help about this problem?
Great thanks!

3

First thing is, always triangulate the track to make the polygon.

  track->SetPoints(m_pPoints);
  track->SetLines(m_pDisplayPlane);

  auto segments = vtkSmartPointer<vtkTriangleFilter>::New();
  segments->SetInputData(track);
  segments->Update();

  auto triangulator = vtkSmartPointer<vtkContourTriangulator>::New();
  triangulator->SetInputData(segments->GetOutput());
  triangulator->Update();

  m_Polygon = triangulator->GetOutput();

But triangulation isn’t enough to properly display the “hole”. You will probably also have to find all the places where the track intersects itself (where line segments cross), generate a new point at every intersection point, and then cut the intersecting line segments in half:

     o                    o
     |                    |
   o-+--o      ->       o-o--o
     |                    |
     o                    o

This would have to be done before the triangulation.

4

Thanks for your advice!
Later I used vtkTriangleFilter and the closed track could be considered as edge and the filter could divide it into bunch of triangles, but the granularity of the triangle seems the reason for the coarse “hole” happening? I tried to recalculate the cross point and update vtkPoints but didn’t make it better, so now I try to interpolate more vtkPoints or sth else make the polygon curve more smooth, in order to fit smaller triangles to fine the “hole”.
Is it workable?

5

Good news! I fixed this problem for smoothing curve with the guidance of https://www.weiy.city/2021/12/vtk-make-interpolation-spline-curve-smoother/. The curve now looks like this:
image

But unfortunately, the triangles could not be generated normally, still generating huge triangles…

image

And now I have a new idea, with the cross point as the dividing line to generate more polygons, with different polygons colored.? Is this ok? But I think this method kinda stupid…