vtkTubeFilter is not able to produce closed loops; behaves unexpectedly if first and last point meet
I already pointed this out on stackoverflow. There somebody said I should probably submit this as a bug.
The issue: Imagine four points in space forming a square. Assign these points to a line that has 5 points, where the last point is the same as the first, thus creating a closed loop. Here is a python code snipped:
pts = vtk.vtkPoints()
pts.SetNumberOfPoints(4)
pts.SetPoint(0, 0.5, 0, 0)
pts.SetPoint(1, 1, 0.5, 0)
pts.SetPoint(2, 0.5, 1, 0)
pts.SetPoint(3, 0, 0.5, 0)
lines = vtk.vtkCellArray()
lines.InsertNextCell(5)
lines.InsertCellPoint(0)
lines.InsertCellPoint(1)
lines.InsertCellPoint(2)
lines.InsertCellPoint(3)
lines.InsertCellPoint(0)
poly = vtk.vtkPolyData()
poly.SetPoints(pts)
poly.SetLines(lines)
tubes = vtk.vtkTubeFilter()
tubes.SetInputData(poly)
tubes.CappingOn()
tubes.SidesShareVerticesOff()
tubes.SetNumberOfSides(4)
tubes.SetRadius(0.1)
tubes.Update()Result. The tubes do not connect, CappingOn() does not change anything. The width of the tubes varies at the end points.
Even if the last and the first point meet on a straight line (by adding a 5th point that lies on one of the sides of the square) the width of the tube changes and it just doesn't look right.