Re: [eigen] Potential unsupported module: Lie Groups

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 07.05.2012 14:19, Hauke Strasdat wrote:
> > I'm afraid you missed a singularity for log of the negative unit quaternion
> > (w=-1, v=0).
> Oh, yes, thanks for that! I checked for singularities using
> "exp(log(x)) = x" tests,
> but thereby I ignored the quaternion double cover. I fixed it and
> updated my tests.

Still not working for w=-1+eps, v!=0. Test with a small v, and make sure 
that log(-exp(v))==v.

> (An atan2-based implementation seems to be a good strategy
> for non-unit quaternions. There is also one in LGSM.)

As pointed out in our paper, you must use atan not atan2 (due to the +/- 
double cover):
http://www.informatik.uni-bremen.de/agbkb/publikationen/bibsearch/detail_e.htm?pk_int=2865, 
Section 3.6.4

Christoph


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Dipl.-Inf. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
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