[vtkusers] closed polygon from splinewidget

[Dean Inglis]

Hi Michael,

vtkSplineWidget gives a shallow copy of the output (vtkPolyData)
from the widget's internal vtkParametricFunctionSource, but that
output is a polyline NOT a polygon, which vtkTriangleFilter expects.
If you know that the output is a closed planar curve, then
just triangulate without recopying.

if ( NewSpline->IsClosed() ) // is it actually geometrically closed?
  {
  vtkPolyData* temp = vtkPolyData::New();
  NewSpline->GetPolyData(temp); // temporarily get the shallow copy

  NewPoly->SetPoints(temp->GetPoints()); // trick to convert polylines to a
polygon
  NewPoly->SetPolys(temp->GetLines());

  triangleFilter->SetInput(NewPoly);
  triangleFilter->Update();
  temp->Delete();
  }
else
  {
   // do something?
  }

Dean




Hi,

I want to probe a dataset with the vtkSplineWidget. But I don't know how to
get the closed surface (inside of closed spline).

I use the vtkSplineWidget to create a closed Spline and get the
corresponding PolyData (->GetPolyData())from the spline. If I visualize it,
I can see that it is a closed Spline (->ClosedOn() was set in
vtkSplineWidget) but only as a line like a Circle or whatever you form with
it.

What I need is the complete Surface e.g. a disk



The way I tried is this:



1.)     create a PolyLine (should be closed) from the PolyData.

2.)     create vtkCellArray and create new polygon from PolyLine and Array

3.)     Tessalate the polgon // gives ERROR



Now when I test to triangulate the new Polygon I get an error that the
vtkTriangleFilter is working on a degenerated polygon.



Here is the code snippet:



       // the spline returns polydata (which can be shown once mapped, it
forms a circle)

       NewSpline->GetPolyData(NewPoly);


       // creating a PolyLine from the polydata (not sure if correct)

       int pointCount = NewPoly->GetPoints()->GetNumberOfPoints();



       aPolyLine = vtkPolyLine::New();

       aPolyLine->GetPointIds()->SetNumberOfIds(pointCount);



       int* pntIds = new int[pointCount];

       for (unsigned int i = 0; i < (int)pointCount; i++)

       {

        pntIds[i] = i;

        }



       aPolyLine->Initialize(pointCount, pntIds, NewPoly->GetPoints());



       vCA = vktCellArray::New();

       vCA->InsertNextCell(aPolyLine);





       // this is from Examples capCow and should create a Polygon from
closed PolyLine ( I also tried the vtkStripper to create a closed PolyLine
but didn’t help)

       tempPoly = vtkPolyData::New();

       tempPoly->SetPoints(aPolyLine->GetPoints());

       tempPoly->SetPolys(vCA);





       triangleFilter->SetInput(tempPoly);

       triangleFilter->Update();  // ERROR vtkPolygon (94564696): Degenerate
polygon encountered during triangulation


Can anybody help?

Thanks alot

Michael