Result vectors on shell

Hello everyone,

I was wondering how the vector for the Result Vectors component are evaluated. I mean the directions of the principal forces come from the associated eigenvectors problem. But how is it possible to define where the arrows points at? As an example for the point P in the figure both vectors a and b satisfies the eigenvector problem.
So I was wondering if the arrows are defined somehow or they are just random since what matters is only the direction itself?

Hello EAnt,
if I remember correctly, the directions are chosen such that the positive angle between the local X-axis of an element and the principal direction are a minimum. A positive angle means counterclockwise rotation about the local Z-axis when you look along the positive Z-axis toward the coordinate origin.