[Chimera-users] inertia axis

[Elaine Meng]

Hi Luca,
"Define Axes"  or command "define axis" gives a cylinder along the major inertia axis.  To have all three (major, intermediate, minor) reported in the Reply Log, instead use the command "measure inertia."  That command always does atom mass-weighting, and by default shows an ellipsoid.

<http://www.cgl.ucsf.edu/chimera/docs/ContributedSoftware/structuremeas/structuremeas.html#axes>
<http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/define.html#axis>
<http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/measure.html#inertia>

I hope this helps,
Elaine
----------
Elaine C. Meng, Ph.D. 
UCSF Computer Graphics Lab (Chimera team) and Babbitt Lab
Department of Pharmaceutical Chemistry
University of California, San Francisco

On Jan 23, 2012, at 7:51 AM, Luca Pellegrini wrote:

> Hello,
> Can you please explain how the inertia axis is calculated in:
> 
> Tools -> Structural analysis -> Structure Measurements -> Define Axes
> 
> when one uses the 'Selected atoms' and 'Mass weighting' option?
> Formally one can define three principal axes of inertia for an object, but only one axis seems to be calculated.
> Thanks,
> Luca
>