VMD-L Mailing List

From: John Stone (johns_at_ks.uiuc.edu)
Date: Tue Jan 27 2009 - 22:29:29 CST

Ed,
  The simplest way to perform rotation transformations on axes
that don't pass through the origin is to first perform a translation
that brings the endpoint of the axis to the origin, then perform the
rotation (about the origin), and then translate back. If I understood
your question correctly, you'd translate by (0,0,-1) first, then
rotate, then translate by (0,0,1) to finish. You should be able to
use this knowledge to form the correct trans command sequence, see
the documentation here:
  http://www.ks.uiuc.edu/Research/vmd/current/ug/node178.html

Cheers,
  John Stone
  vmd_at_ks.uiuc.edu

On Fri, Jan 16, 2009 at 11:49:24AM -0700, Edward Lyman wrote:
> Hi all,
>
> I am trying to rotate a selection about an arbitrary axis which does
> not pass through the origin. It looks like 'trans' routine can give me
> the matrix i need, but i can't figure out which combo of axis, offset,
> center, and origin will do the trick.
>
> let's say i want to rotate 20 degrees about the axis {1,1,1} passing
> through the point {0,0,1}. can anyone give the trans command that will
> give me the matrix i seek?
>
> thx very much,
> Ed 

-- 
NIH Resource for Macromolecular Modeling and Bioinformatics
Beckman Institute for Advanced Science and Technology
University of Illinois, 405 N. Mathews Ave, Urbana, IL 61801
Email: johns_at_ks.uiuc.edu                 Phone: 217-244-3349
  WWW: http://www.ks.uiuc.edu/~johns/      Fax: 217-244-6078