I plotted hundreds of tubes in Paraview and select ‘vary radius by vector’. Now I want to know the relationship between the radius of the tube and the magnitude of the vector. Therefore how can I extract the radius of different part of the tube?

I realised that the radius of blue tubes is larger than that of red tubes and I want to quantify this relationship. All I know now is to extract the coordinate of every point of the tube by using spreadsheet.

The data is the coordinate of the point and the magnitude of the vector. What I want to proof now is that the square of the radius(the cross sectional area of the tube) is inversely proportional to the magnitude of the vector. As the magnitude of the vector varies along the tube, I want to the the exact radius of the tube.

I have to admit, I was really surprised that the radius of the tubes was not proportional to the magnitude of the vector. I had to dig a bit to discover that when you vary the radius by a vector, it adjust the tube to preserve mass flux, which is totally different. I think most users will have the same assumption as myself and @Xinyu_Li, so I raised an issue for it.

Anyway, just to wrap up the conversation, if you want the radius of the tubes to be proportional to the magnitude of the vector, it looks like you first have to use the Calculator filter to compute the magnitude. (For the data shown above, the Calculator expression would be mag(f_59).) Then when the Tube filter is set to Vary RadiusBy Scalar for this value, it should do what you expect.