Bob
Neat indeed! This in itself is a great didactic tool for demonstrating
rotational transformations.
> I'll leave that as a puzzle for you.
I'll cheerfully pass it on to my summer student!
Many thanks again,
Brian
> I think it's just angles and cross products:
>
> var axisC = {0 0 1/1 }
> var axisZ = {0 0 1}
> rotAxis = cross(axisZ,axisC)
> rotAngle = angle(axisZ, {0 0 0},rotAxis, axisC)
> draw {0 0 0} @{rotAxis * 10}
> print " " + rotAngle + " " + rotAxis
> reset
> rotate molecular {0 0 0} @rotAxis @rotAngle
>
> The cross product gets you an axis perpendicular to the other two.
> That trick with the rotAngle done as a dihedral gets you a directed angle
> rather than just a positive value for which you don't know which way to
> turn.
>
> Then you can work out how you want to rotate the others. I'll leave that as
> a puzzle for you.
>
> Bob
>
> On Wed, Jul 1, 2009 at 10:40 AM, Brian McMahon <b...@iucr.org> wrote:
>
> > Is there a neat way (perhaps using quaternions) to view a triclinic
> > unit cell down its crystallographic axes? i.e. a moveto command so
> > that the cell ends up with its c axis normal to the screen and its
> > ac face (in projection) lying horizontally?
> >
> > Thanks
> > Brian
> --
> Robert M. Hanson
> Professor of Chemistry
> St. Olaf College
> 1520 St. Olaf Ave.
> Northfield, MN 55057
> http://www.stolaf.edu/people/hansonr
> phone: 507-786-3107
>
>
> If nature does not answer first what we want,
> it is better to take what answer we get.
>
> -- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
_________________________________________________________________________
Brian McMahon tel: +44 1244 342878
Research and Development Officer fax: +44 1244 314888
International Union of Crystallography e-mail: b...@iucr.org
5 Abbey Square, Chester CH1 2HU, England
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