[vtkusers] Angle between two vectors

[Laurent]

Dear users,

Sorry to dig up this post, but I'm troubled by the results I get.
I used to use the acos() method until I found out that the resulting values
were poor.
We fixed it using the atan2 method instead. Seems working much better!

David (Gobbi), could you elaborate a bit on the error when the angle
approaches 0?
I mean, I get huge differences between both methods. As an example, I get
atan2 Vs acos (in degres):
- 3.67 Vs 10.08
- 11.03 Vs 15.82
- 3.24 Vs 20.02
- 7.78 Vs 20.05
- ...

How to explain these differences?
I've checked if clamp values would give better results but the dot produces
values between -1 and +1.
I've checked multiple times if there was no mistake, and there's not.
I'm horrified!

Since I use the python/numpy distribution from paraview 4.1,
AngleBetweenVectors in not implmented and I had to reimplement the
calculation; That's why I jumped into it more deeply.

Thanks,
Laurent.




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