yade-dev team mailing list archive

[Janek Kozicki <janek_listy@xxxxx>]

Janek Kozicki said:     (by the date of Tue, 26 Oct 2010 18:40:50 +0200)

> Bruno Chareyre said:     (by the date of Tue, 26 Oct 2010 17:09:12 +0200)
> 
> > Below is an example (from revno 2514). If somebody see an obvious reason 
> > for getting a NaN, please let me know; if not, I'll send this to Eigen 
> > (the first line should be enough).

> summarising: it is possible to obtain nan's, if toAxisAngle is not
> taking care of corner cases, and if quaternion diverges too much
> from identity. In your example numbers, the nan was coming from
> arcus_cos(1.00001), which of course must be nan, since acos doesn't
> accept arguments higher than 1.0           

so, for example a function that calculates axis angle, coule 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 growin
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).

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