[vtkusers] Error in Polyline

[Cem DEMiRKIR]

Dear VTK users,
    I constructed some polygonal data and visualized these polylines. But I
got the following error and warning messages 
 
ERROR: In ..\..\Filtering\vtkPolyLine.cxx, line 102
vtkPolyLine (05A503E0): Coincident points in polyline...can't compute
normals
 
Warning: In ..\..\Graphics\vtkTubeFilter.cxx, line 217
vtkTubeFilter (059619B8): Could not generate normals for line. Skipping to
next.

    I would be grateful to anyone who can explain the possible reason(s)
that cause these errors and warnings and How can I isolate or determine the
location of these coincident points in polygonal data ?
 
    Good jobs everyone
    Sincerely
    Cem DEMiRKIR
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