yade-users team mailing list archive

[Václav Šmilauer <eu@xxxxxxxx>]

> I see that there is my formula, which I derived when I was working on
> snow last year. I still remember discussing with Bruno about this
> exact problem :)
> 
> /* Moment Rotation Law */
> Quaternionr delta( b1->state->ori * phys->initialOrientation1.conjugate() *phys->initialOrientation2 * b2->state->ori.conjugate()); //relative orientation

> It calculates rotation difference between two spheres using
> quaternions. The motivation to use both bending and twisting is
> because quaternions cover ALL possible types of rotations.
Just to note that this formula will "fail" if the relative rotation of a
particle will be more than 180 degrees (the quaternion will take it the
other way around, as it goes always the shortest way). 

v