Rotation of Streamlines
General Problem
The AngularVelocity and Rotation fields generated by VTK for streamlines have a wrong scale. If you make a Ribbon, they rotate with the wrong speed. In general angular velocity should be computed as half of Vorticity.
Specific Problem
VTK provides a "Rotation Scale" parameter. But it is not accessible in ParaView. Setting it to -0.5
would get the right Rotation (and right Normal vector for Ribbon).
Solution
It is sufficient to add:
<DoubleVectorProperty command="SetRotationScale"
default_values="1"
label="Rotation Scale"
name="RotationScale"
number_of_elements="1"
panel_visibility="advanced">
<DoubleRangeDomain name="range" />
<Documentation>Scale applied to Vorticity to get AngularVelocity and Rotation</Documentation>
</DoubleVectorProperty>
To all vtkStreamTracer
proxies in ParaViewCore/ServerManager/SMApplication/Resources/filters.xml
Then the "Rotation Scale" will be accessible, and can be set to -0.5
(maybe this should be default?)