[vtkusers] "No vectors defined" error for vtkStreamLine

[Hao Wang]

I'm producing my own vtkPolyData to test one of the vtk classes
implemented by myself. The vtkStreamLine module, which is downstream in
the
pipeline, complains that the vtkPolyData passed to it
has "no vectors defined". I tried to set the vectors by doing
GetPointData().SetVectors() and GetCellPointData().SetVectors(). Neither
way works. Do you know how to fix this problem?

Thanks,
Hao