yade-dev team mailing list archive

[Janek Kozicki <janek_listy@xxxxx>]

Václav Šmilauer said:     (by the date of Tue, 26 Oct 2010 18:58:32 +0200)

> > so, for example a function that calculates axis angle, could do a
> > check if that argument to acos is higher that 1.0. And if yes - then
> > perform a normalization, to bring back down that quaternion to an
> > identity quaternion. This method will prevent quaternions from growing
> > bigger than indentity, but will not catch quaternions that get
> > smaller than identity - and that should be prevented too somehow (but
> > will not produce NaNs).
> 
> I think it should be fixed in eigen, if that is a pure numerics problem.
> That's why we use libs, to not do everything ourselves.

yep, and so I'm glad that Bruno will contact them :)

> What happens if you re-normalize all quaternions before computing the
> product? (just to check; I am not suggesting to do it all the time)

Then a simple thing happens: your quaternions are always good!

Numerical error is a thing that we cannot get rid of, we must live
with it. And it accumulates.

-- 
Janek Kozicki                               http://janek.kozicki.pl/  |