Unexpected behavior of Tube with VaryRadius set to By Vector
When you add the
Tube filter to, say, the output of the stream tracer and then set the
Vary Radius parameter to
By Vector, you get behavior that is probably unexpected for most users.
Based on the labels, I would assume this setup would make the tubes wider for vectors with large magnitude and thinner for tubes with small magnitude (i.e. proportional to the speed). However, this is not what you get. Instead, the slower vectors have a wider radius than the faster vectors.
What is happening is that when you select to
By Vector, you get a mass flux preserving variation. This is mentioned in the VTK filter's doxygen, but not implied by the ParaView labels and not documented anywhere in the ParaView help.
At the very least, the label
By Vector should be changed to help imply the actual behavior. For example, it could say
By Vector (Preserve Mass Flux).
It would also be helpful if a mode was added to
vtkTubeFilter to vary the radius of the tubes proportionally to the magnitude of the vector.